U.S. patent number RE48,439 [Application Number 16/381,423] was granted by the patent office on 2021-02-16 for high voltage tantalum anode and method of manufacture.
This patent grant is currently assigned to Greatbatch Ltd.. The grantee listed for this patent is Greatbatch Ltd.. Invention is credited to Jason T. Hahl, Yanming Liu, Barry C. Muffoletto.
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United States Patent |
RE48,439 |
Liu , et al. |
February 16, 2021 |
High voltage tantalum anode and method of manufacture
Abstract
Tantalum powders produced using a tantalum fiber precursor are
described. The tantalum fiber precursor is chopped or cut into
short lengths having a uniform fiber thickness and favorable aspect
ratio. The chopped fibers are formed into a primary powder having a
controlled size and shape, narrow/tight particle size distribution,
and low impurity level. The primary powder is then agglomerated
into an agglomerated powder displaying suitable flowability and
pressability such that pellets with good structural integrity and
uniform pellet porosity are manufacturable. The pellet is sintered
and anodized to a desired formation voltage. The thusly created
capacitor anode has a dual morphology or dual porosity provided by
a primary porosity of the individual tantalum fibers making up the
primary powder and a larger secondary porosity formed between the
primary powders agglomerated into the agglomerated powder.
Inventors: |
Liu; Yanming (Simpsonville,
SC), Muffoletto; Barry C. (Alden, NY), Hahl; Jason T.
(East Aurora, NY) |
Applicant: |
Name |
City |
State |
Country |
Type |
Greatbatch Ltd. |
Clarence |
NY |
US |
|
|
Assignee: |
Greatbatch Ltd. (Clarence,
NY)
|
Family
ID: |
74555442 |
Appl.
No.: |
16/381,423 |
Filed: |
April 11, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
14479689 |
Apr 12, 2016 |
9312075 |
|
|
|
61874573 |
Sep 6, 2013 |
|
|
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Reissue of: |
15095196 |
Apr 11, 2016 |
9633796 |
Apr 25, 2017 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01G
9/0525 (20130101); B22F 3/24 (20130101); B22F
1/0096 (20130101); H01G 9/0525 (20130101); H01G
9/0032 (20130101); H01G 9/0032 (20130101); B22F
1/0096 (20130101); H01G 9/052 (20130101); B22F
3/1103 (20130101); B22F 5/00 (20130101); H01G
9/052 (20130101); B22F 5/00 (20130101); H01G
9/145 (20130101); B22F 2999/00 (20130101); B22F
2998/10 (20130101); H01G 9/02 (20130101); H01G
9/02 (20130101); B22F 2999/00 (20130101); C22C
1/045 (20130101); B22F 2202/06 (20130101); B22F
3/10 (20130101); B22F 1/004 (20130101); B22F
2998/10 (20130101); H01G 9/145 (20130101); B22F
2003/242 (20130101); B22F 2201/20 (20130101); B22F
2998/10 (20130101); B22F 2999/00 (20130101); B22F
9/04 (20130101); B22F 1/0011 (20130101); B22F
1/0096 (20130101); B22F 1/004 (20130101); B22F
3/02 (20130101); C22C 1/045 (20130101); B22F
3/10 (20130101); B22F 2003/242 (20130101); B22F
2999/00 (20130101); B22F 2999/00 (20130101); B22F
3/10 (20130101); B22F 3/10 (20130101); B22F
2201/11 (20130101); B22F 2201/20 (20130101); B22F
2999/00 (20130101); B22F 1/0096 (20130101); B22F
1/0014 (20130101); B22F 2998/10 (20130101); C22C
1/045 (20130101); B22F 3/02 (20130101); B22F
3/1103 (20130101); B22F 3/10 (20130101); B22F
2003/242 (20130101); B22F 2999/00 (20130101); B22F
5/00 (20130101); B22F 3/1103 (20130101); B22F
2999/00 (20130101); B22F 2003/242 (20130101); B22F
2202/06 (20130101) |
Current International
Class: |
H01G
9/052 (20060101); H01G 9/00 (20060101); B22F
5/00 (20060101); H01G 9/02 (20060101); H01G
9/145 (20060101); B22F 1/00 (20060101); B22F
3/24 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Declaration of David Frost, Inter Partes Review of of U.S. Pat. No.
9,312,075, Petitioner:Composite Materials Technology, Inc.; Case
IPR2017-TBA. cited by applicant .
Petition for Inter Partes Review of U.S. Pat. No. 9,312,075. cited
by applicant .
Tantalum Capacitor Anodes Providing Highest Capacitances: Where Are
the Limits?, Helmut Haas, M. Hagymasi,--CARTS Europe 2011--Nice,
France, Oct. 10-12, 2011., 46-72. cited by applicant .
Substitute Third Party Protest to U.S. Appl. No. 15/596,784 from
CARTS USA 2006. cited by applicant .
Decision Denying Institution of Inter Partes Review in Case
IPR2017-01441 entered Dec. 4, 2017. cited by applicant .
Patent Owners Peliminary Response, Inter Partes Review Case
IPR2017-01441, Sep. 14, 2017. cited by applicant .
Notice of Filing Date accorded to petition and time for filing
patent owner preliminary response, IPR2017-01441,mailed Jun. 14,
2017. cited by applicant .
Decision Denying Petitioner's Request for Rehearing, IPR2017-01441,
entered Mar. 7, 2018. cited by applicant .
Reply to Patent Owner's Preliminary Response Pursuant to 37 CFR.,
IPR2017-01441, Oct. 12, 2017. cited by applicant .
Patent Owners Response to Petitioner's Reply Pursuant to 37 CFR.,
IPR2017-01441, Oct. 18, 2017. cited by applicant .
Decision Denying Institution of Inter Partes Review, IPR2017-01441,
Dec. 4, 2017. cited by applicant .
Substitute Third Party Protest to U.S. Appl. No. 15/596,784.
Petition for Inter Partes Review of U.S. Pat. No. 9,312,075. cited
by applicant .
Substitute Third Party Protest to U.S. Appl. No. 15/596,784. Carts
Europe 2011. cited by applicant .
,Substitute Third Party Protest to U.S. Appl. No. 15/596,784.
Petition for Inter Parties Review of U.S. Pat. No. 9,312,075. cited
by applicant .
Tantalum Capacitor Anodes Providing Highest Capacitance: Where Are
the Limits?, Haas et al., CARTS Europe 2011 in Nice, France Oct.
10, 2011. cited by applicant .
CARTS USA 2006, pp. 229-237, Apr. 3-6, 2006. cited by applicant
.
CARTS Europe 2011, pp. 46-56 and pp. 62-72, ISBN 978-1-62748-085-7.
cited by applicant.
|
Primary Examiner: Torres Velazquez; Norca L.
Attorney, Agent or Firm: Scalise; Michael F.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of U.S. patent
application Ser. No. 14/479,689, filed on Sep. 8, 2014, now U.S.
Pat. No. 9,312,075, which claims priority to U.S. provisional
patent application Ser. No. 61/874,573, filed on Sep. 6, 2013.
Claims
What is claimed is:
1. A capacitor.[.assembly.]., comprising: a) a casing comprising
first and second inner wall surfaces; b) at least a first tantalum
anode housed inside the casing, wherein: i) the first tantalum
anode is characterized as having been fabricated from tantalum
fibers having a diameter ranging from 0.5 .mu.m to 2.5 .mu.m and a
length ranging from 5 .mu.m to 50 .mu.m .Iadd.so that the tantalum
fibers have a length: diameter (L/D) aspect ratio ranging from 2 to
100.Iaddend., the tantalum fibers forming a tantalum powder as a
loosely packed mass of the tantalum fibers, and ii) .Iadd.wherein
.Iaddend.the tantalum powder is characterized as having been
agglomerated into a randomly oriented, substantially non-aligned,
porous agglomerated tantalum powder having a primary .[.porosity.].
.Iadd.density ranging from 1.5 g/cc to 4.5 g/cc.Iaddend., which
agglomerated tantalum powder is characterized as having been
pressed into a tantalum pellet having a secondary .[.porosity.].
.Iadd.density ranging from 4 g/cc to 6.5 g/cc.Iaddend., and iii)
.Iadd.wherein .Iaddend.the tantalum pellet is characterized as
having been sintered so that the .Iadd.sintered tantalum
.Iaddend.pellet has: A) an inter-granule pore size
.Iadd.distribution .Iaddend.attributed to .[.the primary porosity
of.]. .Iadd.a sintered density at.Iaddend.: d10 .[.of.].
.Iadd.ranging from .Iaddend.0.5 .mu.m to 2 .mu.m; and d90 .[.of.].
.Iadd.ranging from .Iaddend.3 .mu.m to 10 .mu.m; and B) an
intra-granule pore size .Iadd.distribution .Iaddend.attributed to
the .[.secondary porosity of.]. .Iadd.sintered density at.Iaddend.:
d10 .[.of.]. .Iadd.ranging from .Iaddend.20 .mu.m to 40 .mu.m; and
d90 .[.of.]. .Iadd.ranging from .Iaddend.60 .mu.m to 100 .mu.m; and
iv) the sintered pellet is characterized as having then been
anodized to a formation voltage greater than zero up to 550 V to
form a dielectric oxide on the tantalum fibers and thereby provide
the tantalum anode; c) an insulative seal comprising a feedthrough
wire electrically connected to the first .Iadd.tantalum
.Iaddend.anode, wherein the feedthrough wire extends outside the
casing and is electrically isolated from the casing; d) a cathode
comprising cathode active material supported by and in electrical
contact with the first inner wall surface and with the second inner
wall surface of the casing; e) a separator preventing direct
physical contact between the first .Iadd.tantalum .Iaddend.anode
and the cathode active material supported on the first and second
inner wall surfaces of the casing while allowing for ion flow
therethrough; and f) an electrolyte contacting the cathode and the
first anode.
2. The capacitor of claim 1.Iadd., .Iaddend.including a second
tantalum anode housed inside the casing, wherein the second
tantalum anode is electrically connected in parallel with the first
tantalum anode, and wherein a cathode current collector comprising
opposed major current collector faces supporting the cathode active
material is disposed intermediate the first and second
.Iadd.tantalum .Iaddend.anodes.
3. The capacitor of claim 1.Iadd., .Iaddend.wherein there are "n"
tantalum anodes electrically connected in parallel with each other
and housed inside the casing, and wherein there are n-1 cathode
current collectors supporting the cathode active material on
opposed major current collector faces thereof and disposed
intermediate side-by-side adjacent ones of the n tantalum
anodes.
4. The capacitor of claim 1.Iadd., .Iaddend.wherein the casing
comprises a first casing member having a first face wall joined to
a surrounding side wall and a second casing member having a second
face wall secured to the surrounding side wall of the first casing
member.
5. The capacitor of claim 1.Iadd., .Iaddend.wherein the feedthrough
wire is connected to the first tantalum anode and a wire extends
from the first tantalum anode to the second tantalum anode to
electrically connect the first and second tantalum anodes in
parallel.
.[.6. The capacitor of claim 1 wherein the tantalum fibers
comprising the tantalum powder have a length-to-diameter (L/D)
aspect ratio ranging from 2 to 100..].
7. The capacitor of claim 1.Iadd., .Iaddend.wherein the tantalum
fibers comprising the tantalum powder have a L/D aspect ratio
ranging from 10 to 40.
8. The capacitor of claim 1.Iadd., .Iaddend.wherein the
agglomerated tantalum powder has substantially no fines less than
200 mesh.
.[.9. The capacitor of claim 1 wherein, prior to being sintered and
anodized to form the first tantalum anode, the tantalum pellet has
a pressed density of 3 g/cc to 8 g/cc..].
.[.10. The capacitor of claim 1 wherein, prior to being sintered
and anodized to form the first tantalum anode, the tantalum pellet
has a pressed density of 4 g/cc to 6.5 g/cc..].
11. The capacitor of claim 1.Iadd., .Iaddend.wherein the tantalum
pellet is characterized as having been sintered at a temperature
ranging from 1,200.degree. C. to 2,200.degree. C., for a time
ranging from 0.1 to 120 minutes, and at a vacuum of
<1.times.10.sup.-4 Torr (Argon).
12. The capacitor of claim 1.Iadd., .Iaddend.wherein the tantalum
pellet is characterized as having been sintered at a temperature
ranging from 1,500.degree. C. to 1,850.degree. C., for a time
ranging from 1 to 10 minutes, and at a vacuum of
<1.times.10.sup.-5 Torr (Argon).
13. The capacitor of claim 1.Iadd., .Iaddend.wherein, prior to
being anodized to form the first tantalum anode, the sintered
tantalum pellet has .[.a.]. .Iadd.the .Iaddend.sintered density
ranging from 4 g/cc to 9 g/cc.
14. The capacitor of claim 1.Iadd., .Iaddend.wherein, prior to
being anodized to form the first tantalum anode, the sintered
tantalum pellet has .[.a.]. .Iadd.the .Iaddend.sintered density
ranging from 5 g/cc to 8 g/cc.
15. The capacitor of claim 1.Iadd., .Iaddend.wherein, prior to
being anodized to form the first tantalum anode, the sintered
tantalum pellet has .[.a d50.]. .Iadd.an .Iaddend.inter-granule
pore size .Iadd.distribution .Iaddend.attributed to the .[.primary
porosity of.]. .Iadd.sintered density at d50 ranging from
.Iaddend.1 .mu.m to 5 .mu.m, and .[.a d50.]. .Iadd.an
.Iaddend.intra-granule pore size .Iadd.distribution
.Iaddend.attributed to the .[.secondary porosity of.].
.Iadd.sintered density at d50 ranging from .Iaddend.30 .mu.m to 80
.mu.m.
.[.16. The capacitor of claim 1 wherein, prior to being pressed
into the tantalum pellet, the agglomerated tantalum powder has an
agglomerate density ranging from 1.5 g/cc to 4.5 g/cc..].
17. The capacitor of claim 1.Iadd., .Iaddend.wherein, prior to
being pressed into the tantalum pellet, the agglomerated tantalum
powder .[.is.]. has .[.an agglomerate.]. .Iadd.a primary
.Iaddend.density ranging from 2.5 g/cc to 3.5 g/cc.
18. The capacitor of claim 1.Iadd., .Iaddend.wherein, prior to
being pressed into the tantalum pellet, the agglomerated tantalum
powder has an agglomerate diameter .[.of.]. .Iadd.distribution
at.Iaddend.: i) d10 of 74 .mu.m; ii) d50 ranging from 200 .mu.m to
500 .mu.m; and iii) d90 of 1,000 .mu.m.
19. The capacitor of claim 1.Iadd., .Iaddend.wherein, prior to
being pressed into the tantalum pellet, the agglomerated tantalum
powder has a d50 .[.inter-granular pore size attributed to the
primary porosity of.]. .Iadd.agglomerate pore size ranging from
.Iaddend.1 .mu.m to 5 .mu.m.
20. The capacitor of claim 1.Iadd., .Iaddend.wherein, prior to
being pressed into the tantalum pellet, the agglomerated tantalum
powder has a d50 .[.inter-granular pore size attributed to the
primary porosity of.]. .Iadd.agglomerate pore size ranging from
.Iaddend.2 .mu.m to 3 .mu.m.
21. The capacitor of claim 1.Iadd., .Iaddend.wherein, prior to
being pressed into the tantalum pellet, the agglomerated tantalum
powder has an .[.inter-granular pore size attributed to the primary
porosity of.]. .Iadd.agglomerate pore size distribution at
.Iaddend.d10 of 0.5 .mu.m and .Iadd.at .Iaddend.d90 of 20
.mu.m.
22. The capacitor of claim 1.Iadd., .Iaddend.wherein the sintered
tantalum pellet is characterized as having been anodized in an
electrolyte comprising H.sub.3PO.sub.4 and having a conductivity up
to about 20,000 .mu.S at 40.degree. C.
23. A capacitor.[.assembly.]., comprising: a) a casing comprising
first and second inner wall surfaces; b) at least a first tantalum
anode and a second tantalum anode electrically connected in
parallel and housed inside the casing, wherein: i) the parallel
connected first and second tantalum anodes are characterized as
each having been fabricated from tantalum fibers having a diameter
ranging from 0.5 .mu.m to 2.5 .mu.m and a length ranging from 5
.mu.m to 50 .mu.m .Iadd.so that the tantalum fibers have a length:
diameter aspect ratio ranging from 2 to 100.Iaddend., the tantalum
fibers forming a tantalum powder as a loosely packed mass of the
tantalum fibers, and ii) .Iadd.wherein .Iaddend.the tantalum powder
is characterized as having been agglomerated into a randomly
oriented, substantially non-aligned, porous agglomerated tantalum
powder having a primary .[.porosity.]. .Iadd.density ranging from
1.5 g/cc to 4.5 g/cc.Iaddend., which agglomerated tantalum powder
is characterized as having been pressed into a first tantalum
pellet and into a second tantalum pellet, both pellets having a
secondary .[.porosity.]. .Iadd.density ranging from 4 g/cc to 6.5
g/cc.Iaddend., and iii) .Iadd.wherein .Iaddend.the first and second
tantalum pellets are characterized as having been sintered so that
the .Iadd.sintered first and second tantalum .Iaddend.pellets each
have: A) an inter-granule pore size .Iadd.distribution
.Iaddend.attributed to .[.the primary porosity of.]. .Iadd.a
sintered density at.Iaddend.: d10 .[.of.]. .Iadd.ranging from
.Iaddend.0.5 .mu.m to 2 .mu.m; .[.and.]. .Iadd.d50 ranging from 1
.mu.m to 5 .mu.m; and.Iaddend. d90 .[.of.]. .Iadd.ranging from
.Iaddend.3 .mu.m to 10 .mu.m; and B) an intra-granule pore size
.Iadd.distribution .Iaddend.attributed to the .[.secondary porosity
of.]. .Iadd.sintered density at.Iaddend.: d10 .[.of.].
.Iadd.ranging from .Iaddend.20 .mu.m to 40 .mu.m; .[.and.].
.Iadd.d50 ranging from 30 .mu.m to 80 .mu.m; and .Iaddend. d90
.[.of.]. .Iadd.ranging from .Iaddend.60 .mu.m to 100 .mu.m; and iv)
the sintered .Iadd.first and second tantalum .Iaddend.pellets are
characterized as having then been anodized to a formation voltage
greater than zero up to 550 V to form a dielectric oxide on the
tantalum fibers and thereby provide the first and second
.Iadd.tantalum .Iaddend.anodes; c) an insulative seal comprising a
feedthrough wire electrically connected to at least the first
.Iadd.tantalum .Iaddend.anode, wherein the feedthrough wire extends
outside the casing and is electrically isolated from the casing; d)
a cathode comprising cathode active material supported by and in
electrical contact with the first inner wall surface and with the
second inner wall surface of the casing; e) a cathode current
collector comprising opposed major current collector faces
supporting the cathode active material and being disposed
intermediate the first and second .Iadd.tantalum .Iaddend.anodes;
f) a separator material preventing direct physical contact between
the first and second .Iadd.tantalum .Iaddend.anodes and the cathode
active material supported on the first and second inner wall
surfaces of the casing, and between the first and second
.Iadd.tantalum .Iaddend.anodes and the cathode active material
supported on the cathode current collector, the separator material
allowing for ion flow through; and g) an electrolyte contacting the
cathode and the first and second anodes.
24. A capacitor.[.assembly.]., comprising: a) a casing comprising
first and second inner wall surfaces; b) "n" tantalum anodes
electrically connected in parallel and housed inside the casing,
wherein: i) the parallel connected n tantalum anodes are each
characterized as having been fabricated from tantalum fibers having
a diameter ranging from 0.5 .mu.m to 2.5 .mu.m and a length ranging
from 5 .mu.m to 50 .mu.m .Iadd.so that the tantalum fibers have a
length: diameter aspect ratio ranging from 2 to 100.Iaddend., the
tantalum fibers forming a tantalum powder as a loosely packed mass
of the tantalum fibers, ii) .Iadd.wherein .Iaddend.the tantalum
powder is characterized as having been agglomerated into a randomly
oriented, substantially non-aligned, porous agglomerated tantalum
powder having a primary .[.porosity.]. .Iadd.density ranging from
1.5 g/cc to 4.5 g/cc.Iaddend., which agglomerated tantalum powder
is characterized as having been pressed into "n" tantalum pellets,
each of the n pellets having a secondary .[.porosity.].
.Iadd.density ranging from 4 g/cc to 6.5 g/cc.Iaddend., and iii)
.Iadd.wherein .Iaddend.the n tantalum pellets are characterized as
having been sintered so that the .Iadd.sintered tantalum
.Iaddend.pellets have: A) an inter-granule pore size
.Iadd.distribution .Iaddend.attributed to .[.the primary porosity
of.]. .Iadd.a sintered density at.Iaddend.: d10 .[.of.].
.Iadd.ranging from .Iaddend.0.5 .mu.m to 2 .mu.m; .[.and.].
.Iadd.d50 ranging from 1 .mu.m to 5 .mu.m; and .Iaddend. d90
.[.of.]. .Iadd.ranging from .Iaddend.3 .mu.m to 10 .mu.m; and B) an
intra-granule pore size .Iadd.distribution .Iaddend.attributed to
the .[.secondary porosity of.]. .Iadd.sintered density at.Iaddend.:
d10 .[.of.]. .Iadd.ranging from .Iaddend.20 .mu.m to 40 .mu.m;
.[.and.]. .Iadd.d50 ranging from 10 .mu.m to 80 .mu.m; and.Iaddend.
d90 .[.of.]. .Iadd.ranging from .Iaddend.60 .mu.m to 100 .mu.m; and
iv) the sintered pellets are characterized as having then been
anodized to a formation voltage .[.greater than zero.]. .Iadd.of at
least 300 V .Iaddend.up to 550 V to form a dielectric oxide on the
tantalum fibers and thereby provide the n tantalum anodes; c) an
insulative seal comprising a feedthrough wire electrically
connected to at least a first one of the n .Iadd.tantalum
.Iaddend.anodes, wherein the feedthrough wire extends outside the
casing and is electrically isolated from the casing; d) a cathode
comprising cathode active material supported by and in electrical
contact with the first inner wall surface and with the second inner
wall surface of the casing; e) n-1 cathode current collectors
housed inside the casing, each cathode current collector comprising
opposed major current collector faces supporting cathode active
material and being disposed intermediate side-by-side adjacent ones
of the n tantalum anodes; f) a separator material preventing direct
physical contact between the tantalum anodes and the cathode active
material supported on the first and second inner wall surfaces of
the casing, and between the tantalum anodes and the cathode active
material supported on the n-1 cathode current collectors, the
separator material allowing for ion flow through; and g) an
electrolyte contacting the cathodes and the anodes.
25. A tantalum anode for incorporation into a capacitor, the
tantalum anode comprising: a) tantalum fibers having a diameter
ranging from 0.5 .mu.m to 2.5 .mu.m and a length ranging from 5
.mu.m to 50 .mu.m .Iadd.so that the tantalum fibers have a length:
diameter aspect ratio ranging from 2 to 100.Iaddend., wherein the
tantalum fibers form a tantalum powder as a loosely packed mass of
the tantalum fibers, and b) .Iadd.wherein .Iaddend.the tantalum
powder is characterized as having been agglomerated into a randomly
oriented, substantially non-aligned, porous agglomerated tantalum
powder having a primary .[.porosity.]. .Iadd.density ranging from
1.5 g/cc to 4.5 g/cc.Iaddend., which agglomerated tantalum powder
is characterized as having been pressed into a tantalum pellet
having a secondary .[.porosity.]. .Iadd.density ranging from 4 g/cc
to 6.5 g/cc.Iaddend., and c) .Iadd.wherein .Iaddend.the tantalum
pellet is characterized as having been sintered so that the
.Iadd.sintered tantalum .Iaddend.pellet has: i) an inter-granule
pore size .Iadd.distribution .Iaddend.attributed to .[.the primary
porosity of.]. .Iadd.a sintered density at.Iaddend.: d10 .[.of.].
.Iadd.ranging from .Iaddend.0.5 .mu.m to 2 .mu.m; .[.and.].
.Iadd.d50 ranging from 1 .mu.m to 5 .mu.m; and.Iaddend. d90
.[.of.]. .Iadd.ranging from .Iaddend.3 .mu.m to 10 .mu.m; and ii)
an intra-granule pore size .Iadd.distribution .Iaddend.attributed
to the .[.secondary porosity of.]. .Iadd.sintered density
at.Iaddend.: d10 .[.of.]. .Iadd.ranging from .Iaddend.20 .mu.m to
40 .mu.m; .[.and.]. .Iadd.d50 ranging from 30 .mu.m to 80 .mu.m;
and.Iaddend. d90 of 60 .mu.m to 100 .mu.m; and d) the sintered
pellet is characterized as having then been anodized to a formation
voltage .[.greater than zero.]. .Iadd.of at least 300 V .Iaddend.up
to 550 V to form a dielectric oxide on the tantalum fibers and
thereby provide the tantalum anode.
26. A method for providing a tantalum anode for an electrolytic
capacitor, the method comprising the steps of: a) providing
tantalum fibers having a diameter ranging from 0.5 .mu.m to 2.5
.mu.m and a length ranging from 5 .mu.m to 50 .mu.m .Iadd.so that
the tantalum fibers have a length: diameter aspect ratio ranging
from 2 to 100.Iaddend.; b) providing a tantalum powder as a loosely
packed mass of the tantalum fibers; c) agglomerating the tantalum
powder into a randomly oriented, substantially non-aligned, porous
agglomerated tantalum powder having a primary .[.porosity.].
.Iadd.density ranging from 1.5 g/cc to 4.5 g/cc.Iaddend.; d)
pressing the agglomerated tantalum powder into a tantalum pellet of
a desired shape, the tantalum pellet having a secondary
.[.porosity.]. .Iadd.density ranging from 4 g/cc to 6.5
g/cc.Iaddend.; e) sintering the tantalum pellet into a coalesced
body of the tantalum fibers to thereby provide a sintered tantalum
pellet having: i) an inter-granule pore size .Iadd.distribution
.Iaddend.attributed to .[.the primary porosity of.]. .Iadd.a
sintered density at.Iaddend.: d10 .[.of.]. .Iadd.ranging from
.Iaddend.0.5 .mu.m to 2 .mu.m; .[.and.]. .Iadd.d50 ranging from 1
.mu.m to 5 .mu.m; and.Iaddend. d90 .[.of.]. .Iadd.ranging from
.Iaddend.3 .mu.m to 10 .mu.m; and ii) an intra-granule pore size
.Iadd.distribution .Iaddend.attributed to the .[.secondary porosity
of.]. .Iadd.sintered density at.Iaddend.: d10 .[.of.].
.Iadd.ranging from .Iaddend.20 .mu.m to 40 .mu.m; .[.and.].
.Iadd.d50 ranging from 30 .mu.m to 80 .mu.m; and.Iaddend. d90
.[.of.]. .Iadd.ranging from .Iaddend.60 .mu.m to 100 .mu.m; and f)
anodizing the sintered tantalum pellet to a formation voltage
greater than zero up to 550 V to form a dielectric oxide on the
tantalum fibers and thereby provide the tantalum anode.
27. The method of claim 26.Iadd., .Iaddend.including providing the
tantalum fibers comprising the tantalum powder having a L/D aspect
ratio ranging from 10 to 40.
28. The method of claim 26.Iadd., .Iaddend.including providing the
agglomerated tantalum powder having substantially no fines less
than 200 mesh.
.Iadd.29. The capacitor of claim 1, wherein the sintered tantalum
pellet is characterized as having been anodized to a formation
voltage that is at least 300 V up to 550 V..Iaddend.
.Iadd.30. The capacitor of claim 23, wherein the first and second
sintered tantalum pellets are characterized as having been anodized
to a formation voltage that is at least 300 V up to 550
V..Iaddend.
.Iadd.31. The method of claim 26, including anodizing the sintered
tantalum pellet to a formation voltage that is at least 300 V up to
550 V..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a valve metal anode for
a capacitor, and more particularly, to an electrolytic capacitor
comprising an anode formed from a pressed pellet of tantalum
fibers. The tantalum fiber pellet is sintered and then anodized
into a high voltage anode at formation voltages up to 550V.
2. Prior Art
Development of powders suitable for making a tantalum capacitor has
been a focus of both capacitor producers and tantalum processors.
Historically, the intent has been to delineate requirements for
tantalum powder that will result in capacitors having reliable
performance, particularly in demanding high voltage applications
such as cardiac defibrillation. It is understood that demanding
applications, such as cardiac defibrillation, require tantalum
powders having suitable surface area, high purity, uniform feature
size, optimized shrinkage, favorable flowability and pressability,
and green pellet strength.
Wet tantalum capacitors have been used in implantable cardiac
defibrillators as the output energy storage capacitor for
delivering the therapeutic electrical shock to the heart to stop a
defibrillation event. These shocks are generally delivered at
voltages ranging from approximately 650 volts to 950 volts. To
achieve therapy delivery at such high voltage levels, between three
and four tantalum capacitors are typically used in the output stage
of the defibrillator.
Several advantages are associated with reducing the number of
capacitors. For example, fewer capacitors required for energy
storage simplifies the device charge and discharge circuits. Also,
a reduction in the number of capacitors results in a reduction in
the number of components in the device. Fewer components mean that
the potential for performance issues decreases, thereby favorably
impacting reliability. Other advantages of fewer components are
more efficient assembly and lower cost.
Accordingly, one purpose of this invention is to develop a
manufacturing process for tantalum anodes that are suitable for
building an electrolytic capacitor for incorporation into a cardiac
defibrillator. The manufacturing processes include pressing,
sintering and forming steps. It is also the purpose of this
invention to fabricate a tantalum anode that is capable of being
formed at higher voltages than is currently known in the prior art.
An anode for high voltage applications such as described within
must also have a pore structure and internal surface area that
allows for low ESR and high capacitance.
It is known in the art that ESR is related to energy loss. It is
also known that for a capacitor, energy loss during charging and
discharging impacts capacitor efficiency. Hence, a lower ESR of an
anode made in accordance with the present invention improves the
efficiency of the capacitor. This is of significance in cardiac
defibrillation as discharge of the capacitor delivers the energy
needed to return the heart to normal rhythm. The improved
efficiency achieved by the present invention enables delivery of
energy and higher voltages, and allows for smaller batteries to be
used in implantable defibrillators due to less energy being
required to charge the capacitors. Improvement in the capacitance
per unit volume of an anode of the present invention allows more
charge to be stored per unit volume, resulting in a capacitor that
stores more energy per unit volume.
When tantalum powders are formed into a porous anode body and then
sintered for use in an electrolytic capacitor, it is known that the
resultant anode capacitance is proportional to the specific surface
area of the sintered porous body. The greater the specific surface
area after sintering, the greater the anode capacitance (.mu.FV/g)
is. Since the anode capacitance (.mu.FV/g) of a tantalum pellet is
a function of the specific surface area of the sintered powder, one
way to achieve a greater net surface area is by increasing the
quantity (grams) of powder per pellet. However, with this approach
cost and size increase considerably. Consequently, cost and size
considerations dictate that tantalum powder development focus on
means to increase the specific surface area of the powder
itself.
Prior art methods for increasing the specific surface area of
tantalum powder include flattening the powder particles into a
flake shape or spherical granulation to produce ovular particle
shapes. For example, U.S. Pat. No. 4,940,490 to Fife et al., U.S.
Pat. No. 5,211,741 to Fife and U.S. Pat. No. 5,580,367 to Fife
disclose flaked tantalum powders and methods for making the flaked
powders. FIG. 1 is an SEM photograph at 5,000.times. showing flake
tantalum particles according to the prior art.
However, efforts to further increase specific surface area by
making thinner tantalum flakes have been hindered by concomitant
loss of processing characteristics. For example, several of the
major deficiencies of very thin tantalum flake are poor flow
characteristics, poor pressability and low green strength, and low
forming voltages. Moreover, increasing particle size using
spherical granulation still tends to result in particles that are
finer than desirable. The resultant pore size and structure of
pellets made from spherical particles tend to be smaller. Pellet
structure damage during high temperature formation is a further
area of concern.
One commonly used tantalum powder having relatively large particles
is commercially available from H. C. Starck under the designation
QR-3. This so called EB melt-type tantalum powder permits anodes to
be made with relatively larger pore structures. The larger pore
structures allow formation electrolytes to cool the interior of the
pellets during formation. However, the relatively small surface
area of these large particle size powders does not result in anodes
of high capacitance per unit volume. That is because the relatively
large particle size results in excessive amounts of tantalum metal
remaining after formation of tantalum oxide. FIG. 2 is an SEM
photograph at 1,000.times. showing EB melt tantalum particles
according to the prior art.
Another commonly used material is available from H. C. Starck as
sodium reduced tantalum powder under the designation NH-175.
Because of its relatively higher surface area, this material is
known to produce anodes with higher capacitance than QR-3 powders.
However, because of its smaller feature size and broad particle
size distribution, NH-175 powders are also known to produce anodes
with smaller pore structures. The smaller pore structure makes
internal cooling of anode pellets during anodization more
difficult, and limits the formation voltages that these anodes can
achieve. If formation voltage gets too high, many of the NH-175
tantalum particles are formed completely through, leaving no
conductive pathways behind the tantalum oxide. FIG. 3 is an SEM
photograph at 5,000.times. showing a sodium reduced NH-175 tantalum
powder agglomerate according to the prior art.
Purity of the powder is another important consideration. Metallic
and non-metallic contamination tends to degrade the dielectric
oxide film in tantalum capacitors. While high sintering
temperatures serve to remove some volatile contaminants, not all
may be removed sufficiently, resulting in sites having high DC
leakage. High DC leakage is known to contribute to premature
electrical failures, particularly in high voltage applications.
Further, high sintering temperatures tend to shrink the porous
anode body, thereby reducing its net specific surface area and thus
the capacitance of the resulting capacitor. Therefore, minimizing
loss of specific surface area under sintering conditions, i.e.,
shrinkage, is necessary in order to produce high .mu.FV/g tantalum
capacitors.
Flowability of tantalum powder and green strength (mechanical
strength of pressed, unsintered powder pellets) are also important
characteristics for a capacitor producer. Not only does flowability
provide for efficient pellet production, it provides for high
volume, automated pellet production. Flowability of agglomerated
tantalum powder is even more essential to production efficiency and
proper operation of automatic pellet presses. Sufficient green
strength permits handling and transport of a pressed product, e.g.,
pellet, without excessive breakage or pellet damage (detectable and
undetectable) that could affect production reject rates and
finished product performance.
Accordingly, what is needed is a tantalum fiber of a strictly
controlled diameter such that sufficient metal remains after
formation to provide a conductive matrix behind the dielectric
oxide. Because of the tightly controlled fiber diameter according
to the present invention, fiber diameter can be minimized to a
greater extent than with other prior art powder types. By
minimizing fiber diameter while ensuring that tantalum is not
totally consumed during formation, the dielectric surface area can
be maximized without isolating dielectric area due to loss of
tantalum substrate.
In that respect, a tantalum anode according to the present
invention is distinguishable from the prior art. Regardless whether
the tantalum is of a flake or spherical shape manufactured by the
beam melt (QR-3 powder) or sodium reduction processes (NH-175
powder), the present invention uniquely discloses the pressing and
sintering of an agglomerate of tantalum fibers having a tightly
controlled aspect ratio. The result is an electrode pellet having a
dual morphology and that is capable of being anodized into a
capacitor anode at formation voltages up to 550V.
SUMMARY OF THE INVENTION
In order to generate high voltage anodes having high capacitance,
and therefore high energy density, anodes having high per unit
surface area must be fabricated. High surface area anodes must also
have pore structures that allow for good internal cooling during
anode formation, and have lower ESR both during formation and
subsequently while in use in the finished capacitor. The use of
tantalum anodes made from tantalum fibers according to the present
invention improves on these issues.
In the present invention, the diameter of the tantalum fibers used
to generate the finished pellet is tightly controlled. First, the
tantalum fibers are divided into desired lengths (up to 50 microns)
to form a randomly oriented, porous powder (primary powder). The
primary powder is subsequently subjected to an agglomeration
process to thereby form an agglomerated powder of the tantalum
fibers. An exemplary agglomeration process is described in U.S.
Pat. No. 5,217,526 to Fife wherein tantalum fibers of the primary
powder are heat treated at 1,000.degree. C. for 30 minutes. The
random agglomerate structure is stabilized by fiber-to-fiber
bonding (sintering). Another agglomeration process is useful with
the present invention is described in U.S. Pat. No. 4,017,302 to
Bates et al. The '526 and '302 patents to Fife and Bates et al. are
incorporated herein by reference. The resulting agglomerated powder
has very narrow particle and pore size distribution. The
agglomerated powder can be pressed into a pellet of a desired shape
comprising the tantalum fibers of the tightly controlled diameter
used to make the primary powder, but with a pellet structure
provided with larger sized pores provided by the agglomeration of
the primary powder. This so called "dual morphology" or dual
porosity pellet structure allows for better electrolyte
penetration. Better electrolyte penetration aids in both cooling of
the pellet during formation as well as lowering the ESR of the
pellet when used as an anode in a capacitor.
These and other objects of the present invention will become
increasingly more apparent to those skilled in the art by reference
to the following detailed description and the appended
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an SEM photograph at 5,000.times. showing flake tantalum
particles according to the prior art.
FIG. 2 is an SEM photograph at 1,000.times. showing EB melt
tantalum particles according to the prior art.
FIG. 3 is an SEM photograph at 5,000.times. showing a sodium
reduced tantalum powder agglomerate according to the prior art.
FIG. 4A is a transverse cross section of a primary billet 10 used
in the production of tantalum fibers.
FIG. 4B is a cutaway view of the primary billet 10 shown in FIG. 4A
revealing the longitudinal disposition of the billet
components.
FIG. 5 is a schematic depiction of the transverse cross section of
the secondary billet 22 used to make tantalum fibers.
FIG. 6 is a schematic depiction showing a cylindrical body
containing a plurality of tantalum fibers.
FIGS. 7 and 8 are SEM photographs at 70.times. and 500.times.,
respectively, showing the present tantalum powder as coarse
agglomerate with high surface area and small pore structure.
FIGS. 9 and 10 are SEM photographs at 1,000.times. and
2,000.times., respectively, showing the present tantalum powder
having a relatively uniform fiber diameter.
FIG. 11 is an SEM photograph at 4,000.times. showing the present
tantalum powder having good random 3-D fiber orientation.
FIG. 12 is an SEM photograph at 10,000.times. showing the present
tantalum powder having good uniform inter-particle spacing.
FIG. 13 is an SEM photograph at 25.times. showing the pore
structure of a pellet pressed from a tantalum powder according to
the present invention.
FIG. 14 is an SEM photograph at 200.times. showing the pore
structure of a pellet pressed from a tantalum powder according to
the present invention.
FIG. 15 is a perspective view of a capacitor 100 according to the
present invention.
FIG. 16 is a perspective view of a dual anode/cathode assembly for
the capacitor 100 shown in FIG. 15.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As defined herein, a fiber is a very fine thread or threadlike
tantalum filament of indefinite length. A primary powder is a mass
of loose tantalum fibers. An agglomerated powder is a mass of
primary powders which have been bonded together through an
agglomeration process by heating the primary powder under
chemically non-reactive conditions to a temperature sufficient to
form stabilized fiber-to-fiber bonding. The resulting tantalum
bodies consist essentially of short relatively uniform diameter
tantalum fibers, bonded and randomly oriented in a substantially
non-aligned, porous array.
As shown in FIGS. 4A and 4B, one process for manufacturing tantalum
fibers for fabricating a tantalum anode that are useful for
building capacitors according to the present invention begins as a
primary billet 10 comprising tantalum rods 12 that have been
inserted into holes 14 drilled longitudinally into a copper matrix
16. In the matrix, copper separates the tantalum rods 12 from each
other. The rods 12 run longitudinally through the body of the
billet and are substantially uniform in diameter and aligned in
parallel. After assembly, a copper nose 18 and tail 20 are welded
onto the primary billet 10, and the billet is then evacuated and
sealed. At this point the primary billet 10 may optionally be hot
or cold isostatically pressed in order to collapse any void space,
thereby promoting filament uniformity.
The primary billet 10 containing the tantalum rods 12 in a copper
matrix 16 is extruded at elevated temperature at a diameter
reduction ratio of approximately 6:1. The resulting rod is cropped
and then drawn down to restack diameter. Annealing may optionally
be performed during drawing should the wire become too stiff or
breakage occurs. Annealing temperatures for tantalum are typically
in the range of 900.degree. C.
At restack diameter, the composite wire is cut into lengths for
assembly into a secondary billet 22 (FIG. 5). The sub-elements 24
made from the primary billet are stacked together with copper rods.
The copper rods are used to form a copper core 26 and an outer
annulus 28. The core 26 and the outer annulus 28 make leaching of
the final composite less difficult. An outer tantalum sheet 30
covers the assembly of sub-elements and copper rods. The sheet 30
is the same length as the rods and it completely surrounds the
filament array. Outside the cylinder of tantalum sheet is an outer
copper can 32.
The secondary billet 22 is assembled, a nose and tail (not shown)
are welded into place, and the billet is evacuated and sealed. The
sealed billet is optionally prepared for extrusion by hot or cold
isostatic pressing in order to collapse any void space within the
billet and to promote filament uniformity. After isostatic
pressing, the secondary billet is machined to fit the extrusion
liner. The billet is then extruded at elevated temperature at a
diameter reduction ratio of 6:1.
The extruded rod is cropped, and the rod is then drawn to a
diameter where the tantalum filament diameter is 5 microns or less.
Again, annealing steps may be employed if necessary. At final size,
the composite tantalum wire is cut into short lengths as
required.
The cut sections are immersed in a solution of nitric acid and
water, and for a period of time sufficient for the acid to fully
leach out the copper core 26 and outer annulus 28, leaving copper
tantalum filaments and the tantalum sheath 32 behind. Since the
tantalum filaments are comparatively tightly spaced, the copper
core 26 and annulus 28 etch away much more rapidly than the copper
separating the filaments. As a result, the acid eventually
surrounds the annulus of tantalum filaments, and then attacks the
filament matrix from all directions, rather than just from the ends
of the cut sections. The total leaching time depend primarily upon
the composite wire diameter and length, with smaller diameters and
greater lengths requiring longer times. After leaching, a plurality
of fine tantalum filaments (<5 micron diameter) surrounded by a
thin tantalum tube 36 is left behind. The tube 36 is removed,
leaving the tantalum filaments 34 behind. The tantalum filaments or
fibers are of an optimum diameter range of 0.5 .mu.m to 2.5 .mu.m.
That the tantalum filaments are of a strictly controlled diameter
range is important for fabrication of an anode according to the
present invention. Not only must the tantalum filaments be of a
prescribed diameter, the above preparation process provides
filaments of a narrow length range and high purity substantially
free of copper.
For more detail regarding production of tantalum filaments that are
useful in the present invention, reference is made to U.S. Pat.
Nos. 4,674,009, 5,034,857, 7,480,978 and 8,858,738, all to Wong and
U.S. Pat. No. 5,869,196 to Wong et al., which are incorporated
herein by reference. Other exemplary processes for forming tantalum
filaments or fibers useful in the present invention are disclosed
in U.S. Pat. Nos. 3,277,564, 3,379,000, 3,394,213, 3,540,114,
3,567,407, 3,698,863, 3,742,369, 3,800,414, 4,502,884, 5,217,526,
5,284,531, 5,245,514, and 5,306,462, the contents of which are
incorporated by reference herein.
FIGS. 7 to 12 are SEM photographs at various magnifications showing
tantalum fibers according to the present invention.
The thusly produced tantalum fibers allow for the generation of
anodes having a dual morphology. This dual morphology provides a
higher surface area material compared to prior art powders. The
term "dual morphology" means there are two pore structures within
the pressed tantalum anode pellet. First, the previously described
tantalum fibers that have been drawn in a tightly controlled manner
to an optimum diameter range of 0.5 .mu.m to 2.5 .mu.m are chopped
to an optimum length ranging from 5 .mu.m to 50 .mu.m. The chopped
fibers have a length-to-width aspect ratio ranging from 2 to 100. A
more preferred aspect length-to-width ratio ranges from 10 to 40.
These fibers form a primary powder as a loosely packed mass of the
tantalum fibers.
Then, an agglomerated powder is formed by subjecting the primary
powder to an agglomeration process. During agglomeration, for
example, the tantalum fibers of the primary powder are heat treated
at 1,000.degree. C. for 30 minutes. This serves to stabilize the
agglomerate structure through fiber-to-fiber bonding (sintering).
As previously discussed, exemplary agglomerating processes are
described U.S. Pat. No. 4,017,302 to Bates et al. and U.S. Pat. No.
5,217,526 to Fife.
Thus, agglomeration serves to bond the primary powders together
into bodies consisting essentially of the short (5 .mu.m to 50
.mu.m) tantalum fibers, bonded and randomly oriented in a
substantially non-aligned, porous array. The tight diameter
distribution of the tantalum fibers in the agglomerated powder
provides a relatively high surface area that is optimally suited to
provide high capacitance per unit volume of a pressed pellet. The
relatively small pores in the primary powder, however, cause higher
ESR than is desirable. The agglomerated powder compensates for this
by providing more open pore structure than in the primary powder
when used to manufacture an anode pellet. Thus, the dual morphology
or dual porosity is the result of the primary porosity between the
individual tantalum fibers making up the agglomerate powder and the
larger secondary porosity formed between the agglomerated powder in
the body of the anode.
Table 1 below provides more detail on powder particle
characteristics. As used this table, a diameter is defined as a
straight line passing from side to side of a tantalum fiber,
through its center.
TABLE-US-00001 TABLE 1 Primary Powder (Fiber) Fiber Diameter
0.5-2.5 .mu.m Fiber Length 5-50 .mu.m L/D Aspect Ratio 2-100
(Preferred Range) 10-40 Agglomerated Particle Agglomerate Density
1.5-4.5 g/cc (Preferred Range) 2.5-3.5 g/cc Agglomerate Dia.
Distribution d50: 200-500 .mu.m d10: 74 .mu.m d90: 1,000 .mu.m
Agglomerate Pore Size d50: 1-5 .mu.m (Preferred Range) d50: 2-3
.mu.m Agglomerate Pore Distribution d10: 0.5 .mu.m d90: 20
.mu.m
Next, the tantalum agglomerate of a pore size from about 1 .mu.m to
5 .mu.m, preferably about 2 .mu.m to about 3 .mu.m comprising a
random distribution of fibers of a diameter of from about 0.5 .mu.m
to about 2.5 .mu.m and of a length of from about 5 .mu.m to about
50 .mu.m is pressed into a pellet of a desired shape. The pellet
contains thousands of the tantalum agglomerates (a plurality). The
pressed anode pellet has a relatively larger pore structure with
lower resistance pathways within. Moreover, this open, lower
resistance structure allows for better cooling of the anode pellet
during the anode formation process avoiding the issues associated
with prior art tantalum anode formation.
A "pellet", as the term is used herein, is a porous mass, body or
structure comprised of agglomerated tantalum powder having the size
and shape characteristics set forth in Table 1. Green strength is a
measure of a pellet's mechanical strength prior to sintering. The
term "pressability" describes the ability of a tantalum powder to
be pressed into a pellet. Tantalum powder that can be formed into
pellets that retain their shape with sufficient green strength to
withstand ordinary processing and manufacturing conditions without
significant breakage have good pressability.
FIGS. 13 and 14 are photographs showing that the present
uniformly-shaped tantalum fibers of the primary and agglomerated
powders are suitable for forming pellet structures having
relatively low compaction densities. The tantalum fibers deform
under smaller forces and interlock with adjacent fibers to provide
pellets with improved green strength. The high green strength also
has an added benefit of permitting an agglomerate with little to no
fines (-200 mesh) material. In commercially available tantalum
powders, fine material often represents 50% or more of the overall
powder volume. In those instances, the fine powder particulate
fills the spaces between the pores and serve to densify the anode
structure. Thus, the fibrous powder allows for an agglomerate
particle having a narrow size distribution with few to none little
fines that when pressed under relatively low force and then
sintered, provides an open network of pores throughout the
anode.
Table 2 below provides more detail on pellet pressing parameters
according to the present invention.
TABLE-US-00002 TABLE 2 Pellet Pressing Conditions Pressed Density
3-8 g/cc (Preferred Range) 4-6.5 g/cc
Following pellet pressing, the green tantalum structure is sintered
by heating to form a coherent body. Sintering is a high temperature
process by which two fibers touching each other at a point contact
coalesce or are fused together. As known by those skilled in the
art, neck growth at the point contact grows to create a new grain
boundary. With sufficient time, the contacting surfaces will
eventually coalesce into a single large contact or contact neck. An
exemplary sintering protocol is described in U.S. Pat. No.
6,965,510 to Liu et al., which is assigned to the assignee of the
present invention and incorporated herein by reference. The '510
Liu et al. patent describes sintering a pressed valve metal pellet
at a relatively high temperature, but for a relatively short
time.
Table 3 below provides more detail on pellet sintering parameters
according to the present invention.
TABLE-US-00003 TABLE 3 Pellet Sintering Conditions Sinter
Temperature 1,200-2,200.degree. C. (Preferred Range)
1,500-1,850.degree. C. Sinter Time 0.1-120 minutes (Preferred
Range) 1-10 minutes Vacuum Level <1 .times. 10.sup.-4 Torr
(Argon) (Preferred Range) <1 .times. 10.sup.-5 Torr (Argon)
Sintered Pellet Sintered Density 4-9 g/cc (Preferred Range) 5-8
g/cc Pellet Pore Size Inter granule d50: 1-5 .mu.m (Preferred
Range) Intra granule d50: 30-80 .mu.m Inter Granule Pore d10: 0.5-2
.mu.m Distribution d90: 3-10 .mu.m Intra Granule Pore d10: 20-40
.mu.m Distribution d90: 60-100 .mu.m
After sintering, the tantalum body is anodized to a desired
formation voltage in an anodizing electrolyte. A suitable anodizing
electrolyte is described in U.S. Pat. No. 6,231,993 to Stephenson
et al., which is assigned to the assignee of the present invention
and incorporated herein by reference. An exemplary anodizing
electrolyte useful with the formation protocols described in the
'993 patent consists of, by volume: about 55% ethylene glycol,
about 44.9% to about 43.5% deionized water and about 0.1% to about
1.5% H.sub.3PO.sub.4. Such an electrolyte has a conductivity of
about 2,500 .mu.S to about 2,600 .mu.S at 40.degree. C. The
conductivity of the formation electrolyte can be increased to
thereby reduce heat generation inside the anode pellet by using an
aqueous electrolyte of H.sub.3PO.sub.4 having a conductivity up to
about 20,000 .mu.S at 40.degree. C.
It is believed in the industry that locally excessive temperatures
and insufficient material transport in porous valve metal bodies
during anodizing (especially for anodization of high voltage,
relatively large, pressed and sintered tantalum powder pellets)
causes breakdown or poor anode electrical properties. Because a
pressed tantalum pellet is porous, anodizing electrolyte is able to
flow into the pellet where it becomes heated during the anodization
process. Heated electrolyte that is unable to readily flow out of
the pellet can cause the temperature of the electrolyte within the
porous structure to increase. It is believed that heated
electrolyte in the porous structure is responsible for cracks,
fissures and similar imperfections as well as crystalline oxide
formed in the oxide coating and inside the tantalum pellet. In
addition to contributing to high DC leakage, these faults degrade
the voltage to which the anode can be charged before breakdown
occurs.
A preferred anodizing method that helps prevent the accumulation of
heated electrolyte inside the tantalum body is to taught in U.S.
Pat. No. 6,231,993 to Stephenson et al., which is assigned to the
assignee of the present invention and incorporated herein by
reference.
U.S. Pat. No. 7,727,372 to Liu et al. describes subjecting the
tantalum body to a current that decreases over time, a formation
voltage that increases over time to a level below the voltage from
the power supply and a power level that is self-adjusted to a level
that decreases excessive heating in the structure. This patent is
assigned to the assignee of the present invention and incorporated
herein by reference. A preferred formation voltage range is at
least 200 V up to 550V. A more preferred range is from 235 V to 480
V. A most preferred formation voltage range is at least 300 V up to
550 V.
Thus, a unimodal agglomerated powder with limited particle size
distribution according to the present invention has multiple
advantages in the formation of a high voltage tantalum anode. A
limited particle distribution provides interstitial gaps between
the particles that promotes electrolyte flow and cooling of the
anode during formation steps. Maintaining a low internal anode
temperature during formation is critical for inhibiting growth of
crystalline tantalum oxide. Furthermore, a highly porous structure
allows for increased formation currents and rates, which increases
production throughput and lessens the entrapment of undesirable
electrolyte constituents. Moreover, the porous anode network
improves conductivity within the final assembled wet capacitor. The
resistance (ESR) within the capacitor is reduced by the low anode
density and open pores. This lower resistance results in higher
efficiencies.
Table 4 below demonstrates the difference in performance properties
of anodes from the prior art QR-3 tantalum powder in comparison to
tantalum fibers according to the present invention.
TABLE-US-00004 TABLE 4 37 C 37 C DC Volume Charge AC Cap ESR Eout1
working Powder (cc) Wt (microF) (Ohms) (J) J/cc J/g voltage Fiber
0.866 5.5 120.86 6.84 9.33 10.76 1.70 400 V Fiber 0.873 5.5 123.20
6.91 9.48 10.86 1.72 400 V QR-3 0.859 6.5 94.74 6.23 7.05 8.21 1.08
400 V Flake QR-3 0.854 6.5 94.68 6.57 7.06 8.27 1.09 400 V
Flake
Referring now to FIGS. 15 and 16, an exemplary capacitor 100
according to the present invention is shown. The capacitor 100
comprises one or more anodes of an anode active material and a
cathode or cathodes of a cathode active material facing adjoining
anode surfaces and housed inside a hermetically sealed casing 102.
The capacitor electrodes are operatively associated with each other
by a working electrolyte (not shown) contained inside the
casing.
The casing 102 comprises first and second metal casing members 104
and 106. The metal casing portions 104, 106 are preferably selected
from the group consisting of tantalum, titanium, nickel,
molybdenum, niobium, cobalt, stainless steel, tungsten, platinum,
palladium, gold, silver, copper, chromium, vanadium, aluminum,
zirconium, hafnium, zinc, iron, and mixtures and alloys thereof.
Preferably, the casing portions 104, 106 have a thickness of about
0.001 to about 0.015 inches.
First casing member 104 is of a drawn metal structure comprising a
first face wall 108 joined to a surrounding side wall 110 extending
to an edge 112. Additionally, casing portion 104 can be of a
machined construction or be formed by a metal injection molding
process. Second casing member 106 is in the shape of a plate and
comprises a second face wall 114 having a surrounding edge 116. The
casing members 104 and 106 are hermetically sealed together by
welding the overlapping edges 112 and 116 where they contact each
other. The weld 118 is provided by any conventional means; however,
a preferred method is by laser welding.
A feedthrough 120 electrically insulates an anode terminal wire 122
from the casing 12. The terminal wire 122 extends from within the
casing 102 to the outside thereof. The location of a hole 124 in
the surrounding side wall 110 of the casing member 104 into which
the feedthrough 120 is mounted is either offset towards the front
edge 112, offset towards the face wall 108, or centered between the
face wall 108 and the front edge 112. The hole 124 is in alignment
with an embedded wire of one of the anodes, as will be described
subsequently.
According to an exemplary embodiment, the feedthrough 120 comprises
an insulating material 128, for example glass, ceramic, polymer, or
epoxy. Regardless the insulating material, the feedthrough 120
comprises a ferrule 126 defining an internal cylindrical through
bore or passage of constant inside diameter. The insulating
material 128 seals between a bore of the ferrule 126 and the anode
terminal wire 122 passing therethrough from inside the casing 12.
The feedthrough 120 may also prevent material, for example,
electrolyte from escaping the casing 12 and prevent foreign
material from entering the casing 12 in the location of the anode
terminal wire 122. The terminal wire 122 has a J-shaped interior
portion 130 for connection to one or more anode wires within casing
102. A suitable glass for insulative seal 128 is, for example,
ELAN.RTM. type 88 or MANSOL.TM. type 88.
Capacitor 100 further comprises an anode assembly one or more
anodes made as previously described and connected to the terminal
wire 122 of feedthrough 120 within the casing 102. The anode
assembly includes a first anode pellet 132 and a second anode
pellet 134. The first anode pellet 132 comprises an inner major
face wall 136 and an outer major face wall 138, both extending to a
surrounding edge 140. Similarly, the second anode pellet 134
comprises an inner major face wall 142 and an outer major face wall
144, both extending to a surrounding edge 146.
An anode wire 148 that is partially embedded in the first anode
pellet 132 has a distal end 148A that is electrically connected to
the J-shaped interior portion 130 of the terminal wire 122. The
anode wire 148 is preferably of tantalum. As previously described,
the tantalum anode pellets 132 and 134 are sintered under a vacuum
at high temperatures and then anodized in a suitable electrolyte.
The anodizing electrolyte fills the pores of the tantalum pellets
132, 134 and a continuous dielectric oxide is formed thereon. In
that manner, the anode pellets 132, 134 and extending wire 148 are
provided with a dielectric oxide layer formed to a desired working
or formation voltage.
A second U-shaped wire has an end portion 150A embedded in the
first pellet 132 and a second end portion 150B embedded in the
second pellet 134. The second wire has an exposed U-shaped portion
150C. Thus, the U-shaped anode wire is not directly connected to
the terminal wire 122 or to the wire 148 of anode pellet 132.
Instead, it connects directly to the first and second anode pellets
132, 134, and continuity to the embedded wire 148 is through the
active material of the first anode pellet 132. In this manner, the
anode pellets 132 and 134 are connected to terminal wire 122 in
series.
After the anode pellet 132 and extending wire 148 are anodized to
the desired formation voltage, the dielectric oxide is removed from
the wire. The wire 148 is subsequently connected to an anode lead
122 supported in an insulative material of the insulative seal 120.
Laser welding secures the wire 122 and lead 148 together. The wire
148 and connected lead 122 are then re-anodized.
The U-shaped anode wire bridging between anode pellets 132, 134 and
the feedthrough of wire 122 including its J-shaped portion 130
joined to the distal end 148A of wire 148 is enclosed and
immobilized within a molded polymer (not shown). The various anode
wires, whether embedded or not, are preferably positioned near the
central regions of the respective anode pellets 132 and 134, i.e.,
equidistant from the inner and outer face walls of the pellets.
The cathode of capacitor 100 comprises cathode active material
supported by and in contact with the face walls of the casing
members 102 and 104. More particularly, cathode active material
contacts the inner surfaces of the respective casing face walls 108
and 114 in a pattern that generally mirrors the shape of the anode
pellets 132 and 134. The cathode active material has a thickness of
about a few hundred Angstroms to about 0.1 millimeters and is
either directly coated on the inner, surfaces of the face walls
108, 114 or it is coated on a conductive substrate (not shown)
supported on and in electrical contact with the inner surfaces
thereof.
Another portion of the cathode active material is positioned
intermediate the anodes 132 and 134. The intermediate cathode
active material is supported on opposed surfaces of a cathode
current collector 152, preferably in the form of a foil. That way,
the cathode current collector 152 having opposed first and second
major faces provided with cathode active material thereon is
positioned opposite the first and second anodes 132 and 134,
thereby forming an anode-cathode assembly. A tab 152A is provided
on current collector 152 for tack welding to the inner surface of
the face wall 108, surrounding side wall 110 of casing member 104,
or to the second face wall 114. The tab 152A is bent approximately
perpendicular to the respective surrounding edges 140 and 146 of
anode pellets 132 and 134 to position it for welding to side wall
110. The casing 102 comprising members 104, 106 serves as the
cathode terminal.
In that respect, the face walls 108, 114 of the casing portions
132, 134 may be of an anodized-etched conductive material, have a
sintered active material with or without oxide contacted thereto,
be contacted with a double layer capacitive material, for example a
finely divided carbonaceous material such as graphite, activated
carbon, carbon or platinum black, a redox, pseudocapacitive or an
under potential material, or be an electroactive conducting polymer
such as polyaniline, polypyrrole, polythiophene, polyacetylene, and
mixtures thereof.
According to one preferred aspect of the present invention, the
redox or cathode active material includes an oxide of a first
metal, the nitride of the first metal, the carbon nitride of the
first metal, and/or the carbide of the first metal, the oxide,
nitride, carbon nitride and carbide having pseudocapacitive
properties. The first metal is preferably selected from the group
consisting of ruthenium, cobalt, manganese, molybdenum, tungsten,
tantalum, iron, niobium, iridium, titanium, zirconium, hafnium,
rhodium, vanadium, osmium, palladium, platinum, nickel, and
lead.
A pad printing process as described in U.S. Pat. No. 7,116,547 is
one method for making such a coating. An ultrasonically generated
aerosol as described in U.S. Pat. Nos. 5,894,403, 5,920,455,
6,224,985, and 6,468,605, all to Shah et al., is also a suitable
deposition method. These are assigned to the assignee of the
present invention and incorporated herein by reference. Other
processes for depositing cathode material that are useful with the
present invention include screen printing as well as ink jet
printing. Standard aerosol spraying can also be used.
The capacitor 100 preferably comprises separators of electrically
insulative material that completely surround and envelop the anode
pellets 132, 134. For example, a first separator 154 encloses the
first anode 132 and a second separator 156 encloses the second
anode pellet 134. The separators 154, 156 may be formed as pouches
that enclose the respective anode pellets 132, 134. In particular,
separator 154 is sealed at a flap 158 of material that extends
around the majority of the perimeter of anode pellet 132 except at
the feedthrough wire 148A and embedded wire 150A. In like manner,
separator pouch 156 is sealed at a flap 160 of material that
extends around the majority of the perimeter of anode pellet 134
with anode wire 150B extending therefrom. The individual sheets of
separator material are closed at flaps 158 and 160 by a process
such as ultrasonic welding, or heat sealing.
The separators 154 and 156 prevent an internal electrical short
circuit between the anode and cathode active materials in the
assembled capacitor and have a degree of porosity sufficient to
allow ion flow therethrough during the charge and discharge of the
capacitor 100. Illustrative separator materials include woven and
non-woven fabrics of polyolefinic fibers including polypropylene
and polyethylene or fluoropolymeric fibers including polyvinylidene
fluoride, polytetrafluoroethylene, and
polyethylenechlorotrifluoroethylene laminated or superposed with a
polyolefinic or fluoropolymeric microporous film, non-woven glass,
glass fiber materials and ceramic materials. Additional separator
materials may include films of poly sulfone and polyester, for
example, polyethylene terephthalate. Suitable microporous films
include a polyethylene membrane commercially available under the
designation SOLUPOR.RTM. (DMS Solutech), a polytetrafluoroethylene
membrane commercially available under the designation ZITEX.RTM.
(Chemplast Inc.) or EXCELLEPATOR.RTM. (W. L. Gore and Associates),
a polypropylene membrane commercially available under the
designation CELGARD.RTM. (Celanese Plastic Company, Inc.), and a
membrane commercially available under the designation DEXIGLAS.RTM.
(C. H. Dexter, Div., Dexter Corp.). Cellulose based separators are
also useful. Depending on the electrolyte used, the separator 18
can be treated to improve its wettability, as is well known by
those skilled in the art. A preferred separator structure 18
comprises a non-woven layer of polyethylene or polypropylene, a
microporous layer of polyethylene or polypropylene, and, possibly a
third layer of polyethylene or polypropylene, which is also
non-woven. Regardless its material of construction, the separator
must be protected from the heat generated when casing portion 104
is secured to casing portion 106 by weld 118.
In a final step of providing capacitor 100, the void volume in
casing 102 is filled with a working electrolyte (not shown) through
a fill opening 162. This hole is then welded closed to complete the
sealing process. A suitable working electrolyte for the capacitor
10 is described in U.S. Pat. No. 6,219,222 to Shah et al., which
includes a mixed solvent of water and ethylene glycol having an
ammonium salt dissolved therein. U.S. Pat. No. 6,687,117 to Liu and
U.S. Patent Application Pub. No. 2003/0090857 describe other
electrolytes for the present capacitor 100. The electrolyte of the
latter publication comprises water, a water-soluble inorganic
and/or organic acid and/or salt, and a water-soluble nitro-aromatic
compound while the former relates to an electrolyte having
de-ionized water, an organic solvent, isobutyric acid and a
concentrated ammonium salt. These patents and publication are
assigned to the assignee of the present invention and incorporated
herein by reference.
While capacitor 100 has been described as comprising cathode
current collector 152 supporting cathode active material on its
opposite major sides and positioned intermediate the parallel
connected anodes 132 and 134 that is by way of example. Those
skilled in the art will readily understand that a capacitor
according to the present invention can further have three or more
to "n" anodes connected in parallel with each other by bridging
U-shaped anode wires (150A, 150B and 150C). There will be cathode
active material supported on the inner surfaces of the casing walls
108, 114 and facing the first and the n.sup.th anodes.
For a more detailed description of an exemplary capacitor useful
with the tantalum fibers according to the present invention,
reference is made to U.S. Pat. No. 7,483,260 to Ziarniak et al. The
'260 patent is assigned to the assignee of the present invention
and incorporated herein by reference.
Thus, it should be apart to those of ordinary skill in the art that
the uniqueness of the present invention is the ability to press an
anode pellet having good integrity, good pore structure and that is
capable of being formed at high voltages. Resultant from this is
the ability to design and fabricate capacitors with higher voltages
vs. the prior art. That is because the anodes of the present
invention have higher energy density and substantially low ESR in
comparison to those made according to the prior art. This is
achieved by the present invention through the use of the starting
tantalum fiber material and the specific processing that creates
this anodized anode body.
Although several embodiments of the invention have been described
in detail, for purposes of illustration, various modifications of
each may be made without departing from the spirit and scope of the
invention. Accordingly, the invention is not to be limited, except
as by the appended claims.
* * * * *