U.S. patent application number 10/303622 was filed with the patent office on 2003-04-24 for high rate batteries.
This patent application is currently assigned to NanoGram Corporation. Invention is credited to Banfol, Devendra R., Chaloner-Gill, Benjamin, Chiruvolu, Shivkumar, Cornell, Ronald M., Ghantous, Dania I., Hoang, Khanh, McGovern, William E., Pinoli, Allison A..
Application Number | 20030077513 10/303622 |
Document ID | / |
Family ID | 24606080 |
Filed Date | 2003-04-24 |
United States Patent
Application |
20030077513 |
Kind Code |
A1 |
Ghantous, Dania I. ; et
al. |
April 24, 2003 |
High rate batteries
Abstract
Improved high rate batteries based on silver vanadium oxide
yield improved pulsed performance. In particular, batteries
comprise an electrolyte having lithium ions and a cathode
comprising silver vanadium oxide. Improved batteries have a pulsed
specific energy of at least about 575 mWh/g when pulsed in groups
of four-10 second pulses at a current density of 25 mA/cm.sup.2
spaced by 15 seconds between pulses and with 30 minutes between
pulse groups down to a discharge voltage of 1.5 volts. In addition,
improved batteries can achieve high maximum specific powers, high
current densities and no voltage delay in pulsed operation. The
batteries are particularly suitable for use in implantable medical
devices, such as, defibrillators, pacemakers or combinations
thereof. Improved processing approaches are described.
Inventors: |
Ghantous, Dania I.; (San
Jose, CA) ; Chaloner-Gill, Benjamin; (San Jose,
CA) ; Chiruvolu, Shivkumar; (Sunnyvale, CA) ;
Banfol, Devendra R.; (Fremont, CA) ; McGovern,
William E.; (LaFayette, CA) ; Cornell, Ronald M.;
(Livermore, CA) ; Hoang, Khanh; (San Jose, CA)
; Pinoli, Allison A.; (Sunnyvale, CA) |
Correspondence
Address: |
Patterson, Thuente, Skaar & Christensen, P.A.
4800 IDS Center
80 South 8th Street
Minneapolis
MN
55402-2100
US
|
Assignee: |
NanoGram Corporation
|
Family ID: |
24606080 |
Appl. No.: |
10/303622 |
Filed: |
November 25, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10303622 |
Nov 25, 2002 |
|
|
|
09649752 |
Aug 28, 2000 |
|
|
|
6503646 |
|
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Current U.S.
Class: |
429/219 ;
429/217; 429/231.5; 429/231.95 |
Current CPC
Class: |
C01P 2002/88 20130101;
H01M 10/052 20130101; H01M 4/622 20130101; Y02E 60/10 20130101;
C01G 31/00 20130101; C01P 2002/72 20130101; H01M 4/34 20130101;
H01M 2004/021 20130101; C01P 2006/12 20130101; H01M 4/54 20130101;
H01M 4/625 20130101; H01M 4/485 20130101 |
Class at
Publication: |
429/219 ;
429/231.5; 429/231.95; 429/217 |
International
Class: |
H01M 004/54; H01M
004/58; H01M 004/40 |
Claims
What is claimed is:
1. A battery comprising an electrolyte comprising lithium ions and
a cathode comprising silver vanadium oxide particles, the battery
exhibiting no significant voltage delay near 2.6 volts.
2. The battery of claim 1 wherein the electrical resistance does
not increase substantially upon discharge to 1.5 volts.
3. The battery of claim 1 wherein the cathode comprises at least
about 10 weight percent electrically conductive, electro-chemically
inert particles.
4. The battery of claim 1 wherein the silver vanadium oxide
particles have an average diameter less than about 1000 nm.
5. The method of claim 1 wherein the silver vanadium oxide
particles have an average diameter less than about 500 nm.
6. The battery of claim 1 wherein silver vanadium oxide particles
comprise Ag.sub.xV.sub.2O.sub.y, with 0.3.ltoreq.x.ltoreq.2.0 and
4.5.ltoreq.y.ltoreq.6.0.
7. The battery of claim 1 having a pulse specific energy of at
least about 600 mWh/g.
8. The battery of claim 1 having a pulse specific capacity of at
least about 275 mAh/g to 1.5 volts.
9. The battery of claim 1 having a maximum pulse specific power of
at least about 1.5W/g to 1.5 volts.
10. The battery of claim 1 wherein the anode comprises lithium
metal foil.
11. The battery of claim 1 wherein the anode comprises lithium
metal particles.
12. The battery of claim 1 wherein pulse trains can be supplied by
the battery at current densities greater than about 50
mA/cm.sup.2.
13. The battery of claim 1 wherein the cathode has a thickness of
at least about 0.8 mm.
14. The battery of claim 1 wherein the cathode has a density from
about 1.8 g/cc to about 2.8 g/cc.
15. An implantable medical device comprising a battery of claim
1.
16. An implantable medical device of claim 15 having defibrillating
function.
17. An implantable medical device of claim 15 having defibrillating
and cardiac pacing functions.
18. A method for producing an electrode, the method comprising:
mixing with low shear in a homogenizer, a composition comprising
silver vanadium oxide particles, electrically conductive particles,
binder and solvent; and forming the mixed composition into an
electrode.
19. The method of claim 18 wherein the silver vanadium oxide
particles have an average diameter less than about 1000 nm.
20. The method of claim 18 wherein the electrically conductive
particles comprise conductive carbon.
21. The method of claim 18 wherein the binder comprises a polymer
selected from the group consisting of polyvinylidene fluoride,
polyethylene oxide, polyethylene, polypropylene, polytetrafluoro
ethylene, polyacrylates, ethylene-(propylene-diene monomer)
copolymer (EPDM) and mixtures and copolymers thereof.
22. The method of claim 18 wherein the solvent is selected from the
group consisting of propylene carbonate, dimethyl carbonate,
diethyl carbonate, 2-methyl tetrahydrofuran, dioxolane,
tetrahydrofuran, 1, 2-dimethoxyethane, ethylene carbonate,
.gamma.-butyrolactone, dimethyl sulfoxide, acetonitrile, formamide,
dimethyl formamide, nitromethane, diglyme, triglyme, methyl ethyl
carbonate and mixtures thereof.
23. The method of claim 18 wherein shear is provided by a
homogenizer mixing at a rate from about 8000 rpm to about 24,000
rpm.
24. The method of claim 18 further comprising incorporating a metal
current collector into the electrode.
25. The method of claim 24 wherein the current collector comprises
a metal grid.
26. A method for forming a battery, the method comprising producing
a cathode according to the method of claim 18.
27. The method of claim 26 wherein the battery comprises an anode
comprising elemental lithium metal.
28. The method of claim 26 further comprising placing a separator
between the cathode and an anode.
29. The method of claim 28 wherein the separator comprises a porous
polymer or a solid electrolyte.
30. The method of claim 26 wherein the battery comprises a
plurality of cathodes.
31. A battery comprising a cathode having silver vanadium oxide
particles, a binder and at least about 10 weight percent
electrically conductive, electro-chemically inert particles,
wherein the cathode has a thickness of at least about 0.8 mm.
32. The battery of claim 31 wherein the cathode comprises at least
about 15 weight percent electrically conductive, electrochemically
inert particles.
33. The battery of claim 31 wherein the cathode comprises at least
about 20 weight percent electrically conductive, electrochemically
inert particles.
34. The battery of claim 31 wherein the anode comprises lithium
metal and the battery exhibits no significant voltage delay under
pulsed operation at about 2.6 volts.
35. The battery of claim 31 wherein the electrical resistance does
not increase substantially upon discharge to 1.5 volts.
36. The battery of claim 31 wherein the electrically conductive,
electrochemically inert particles comprise silver particles with an
average diameter less than 1000 nm.
37. The battery of claim 31 wherein the electrically conductive,
electrochemically inert particles comprise carbon particles.
38. The battery of claim 31 wherein the cathode has a density from
about 1.8 g/cc to about 2.8 g/cc.
39. The battery of claim 31 wherein the battery can supply current
pulses at a rate of at least 50 mA/cm.sup.2.
40. The battery of claim 31 having a pulse specific capacity of at
least about 275 mAh/g to 1.5 volts.
41. The battery of claim 31 wherein the anode comprises elemental
lithium metal.
42. An implantable medical device comprising a battery of claim
31.
43. A battery comprising a cathode comprising silver vanadium oxide
particles, a binder and at least about 10 weight percent
electrically conductive, electro-chemically inert particles,
wherein the cathode has a density from about 1.8 g/cc to about 2.8
g/cc.
44. The battery of claim 43 wherein the cathode comprises at least
about 15 weight percent electrically conductive, electrochemically
inert particles.
45. The battery of claim 43 wherein the cathode has a density from
about 2.4 g/cc to about 2.8 g/cc.
46. The battery of claim 43 wherein the electrical resistance does
not increase substantially upon discharge to 1.5 volts.
47. The battery of claim 43 wherein the anode comprises lithium
metal and the battery exhibits no significant voltage delay under
pulsed operation at about 2.6 volts.
48. The battery of claim 43 wherein the electrically conductive,
electrochemically inert particles comprise carbon particles.
49. The battery of claim 43 further comprising an anode wherein the
anode comprises elemental lithium metal.
50. The battery of claim 43 wherein the silver vanadium oxide
particles have an average diameter less than about 1000 nm.
51. The battery of claim 43 wherein the silver vanadium oxide
particles comprise Ag.sub.xV.sub.2O.sub.y, with
0.3.ltoreq.x.ltoreq.2.0 and 4.5.ltoreq.y.ltoreq.6.0.
52. The battery of claim 43 having a pulse specific capacity of at
least about 275 mAh/g to 1.5 volts.
53. The battery of claim 43 wherein the binder comprises
polyvinylidene fluoride, polyethylene oxide, polyethylene,
polypropylene, polytetrafluoro ethylene, polyacrylates,
ethylene-(propylene-diene monomer) copolymer (EPDM), mixtures
thereof or copolymers thereof.
54. An implantable medical device comprising the battery of claim
43.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of copending U.S. patent
application Ser. No. 09/649,752 to Ghantous et al., entitled "High
Rate Batteries," incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The invention relates to batteries having very high rate
capabilities. More particularly, the invention relates to batteries
having metal vanadium oxides that can produce extremely high
current densities. These batteries are particularly useful for
implantable medical devices, especially defibrillators.
[0003] Lithium-based batteries have become commercially successful
due to their relatively high energy density. Suitable positive
electrode materials for lithium-based batteries include materials
that can intercalate lithium atoms into their lattice. The negative
electrode can be lithium metal, lithium alloys or compounds that
can reversibly intercalate lithium atoms into their lattice. In
conventional terminology, lithium-based batteries formed from
lithium metal or lithium alloy negative electrodes are referred to
as lithium batteries while batteries formed with an anode (negative
electrode) active material that can intercalate lithium ions are
referred to as lithium ion batteries.
[0004] In order to produce improved batteries, various materials
have been examined for use as cathode (positive electrode) active
materials for lithium based batteries. A variety of materials,
generally chalcogenides, are useful in lithium based batteries. For
example, vanadium oxides in certain oxidation states are effective
materials for the commercial production of positive electrodes for
lithium based batteries. Also, metal vanadium oxide compositions
have been identified as having high energy densities and high power
densities, when used in positive electrodes for lithium based
batteries. Silver vanadium oxide has a particularly high energy
density and high power densities, when used in lithium based
batteries. Silver vanadium oxide batteries have found particular
use in the production of implantable cardiac defibrillators where
the battery must be able to recharge a capacitor to deliver large
pulses of energy in rapid succession.
SUMMARY OF THE INVENTION
[0005] In a first aspect, the invention pertains to a battery
comprising an electrolyte having lithium ions and a cathode
comprising silver vanadium oxide particles. The battery has a
pulsed specific energy of at least about 575 mWh/g when pulsed in
groups of four-10 second pulses at a current density of 25
mA/cm.sup.2 spaced by 15 seconds between each pulse and with 30
minutes between pulse groups down to a pulse discharge voltage of
1.5 V. The battery can be used in a defibrillator, a pacemaker or a
combination thereof.
[0006] In another aspect, the invention pertains to a battery
comprising silver vanadium oxide particles. The battery has a
maximum pulse specific power of greater than about 1.5 W/g to 1.5
V.
[0007] Moreover, the invention pertains to a method for producing
silver vanadium oxide particles, the method comprising heating a
mixture of vanadium oxide powder and a silver compound in a vessel
with agitation of the reactants.
[0008] In addition, the invention pertains to a method for
producing an electrode, the method including mixing a battery
composition with low shear in a homogenizer and forming the mixed
composition into an electrode. The battery composition comprises
silver vanadium oxide particles, electrically conductive particles,
binder and solvent.
[0009] In another aspect, the invention pertains to a battery
comprising an anode comprising lithium metal foil, a cathode
comprising silver vanadium oxide particles and an electrolyte
having a solvent comprising alkylene carbonate and at least about
25 percent by volume 1,2-dimethoxyethane.
[0010] In a further aspect, the invention pertains to a method of
producing vanadium oxide particles, the method comprising reacting
a reactant stream comprising a vanadium precursor and water,
wherein there is insufficient O.sub.2 to form the vanadium oxide
product.
[0011] Furthermore, the invention pertains to a battery comprising
a cathode having silver vanadium oxide particles, a binder and at
least about 10 weight percent electrically conductive,
electrochemically inert particles. The cathode has a thickness of
at least about 0.8 mm.
[0012] In other embodiments, the invention pertains to a battery
comprising a cathode having silver vanadium oxide particles, a
binder and at least about 10 weight percent electrically
conductive, electro-chemically inert particles. The cathode has a
silver vanadium oxide density from about 1.8 g/cc to about 2.8
g/cc.
[0013] Moreover, the invention pertains to a battery comprising an
electrolyte having lithium ions and a cathode comprising silver
vanadium oxide particles, the battery being able to produce pulse
trains with current densities of at least about 50 mA/cm.sup.2.
[0014] In addition, the invention pertains to a battery comprising
an electrolyte having lithium ions and a cathode comprising silver
vanadium oxide particles, the battery exhibiting no significant
voltage delay near 2.6 volts in pulse operation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a schematic, sectional view of an embodiment of a
laser pyrolysis apparatus, where the cross section is taken through
the middle of the laser radiation path. The upper insert is a
bottom view of the exit nozzle, and the lower insert is a top view
of the injection nozzle.
[0016] FIG. 2 is a schematic, side view of a reactant delivery
apparatus for the delivery of vapor reactants to the laser
pyrolysis apparatus of FIG. 1.
[0017] FIG. 3 is a schematic, side view of a reactant delivery
apparatus for the delivery of an aerosol reactant to the laser
pyrolysis apparatus of FIG. 1.
[0018] FIG. 4 is a perspective view of an alternative embodiment of
a laser pyrolysis apparatus.
[0019] FIG. 5 is a sectional view of the inlet nozzle of the
alternative laser pyrolysis apparatus of FIG. 4, the cross section
being taken along the length of the nozzle through its center.
[0020] FIG. 6 is a sectional view of the inlet nozzle of the
alternative laser pyrolysis apparatus of FIG. 4, the cross section
being taken along the width of the nozzle through its center.
[0021] FIG. 7 is a perspective view of an embodiment of an
elongated reaction chamber for performing laser pyrolysis.
[0022] FIG. 8 is a perspective view of an embodiment of an
elongated reaction chamber for performing laser pyrolysis.
[0023] FIG. 9 is a cut away, side view of the reaction chamber of
FIG. 8.
[0024] FIG. 10 is a partially sectional, side view of the reaction
chamber of FIG. 8, taken along line 10-10 of FIG. 8.
[0025] FIG. 11 is a fragmentary, perspective view of an embodiment
of a reactant nozzle for use with the chamber of FIG. 8.
[0026] FIG. 12 is a schematic, sectional view of an apparatus for
heat treating nanoparticles, in which the section is taken through
the center of the apparatus.
[0027] FIG. 13 is a schematic, perspective view of a battery of the
invention.
[0028] FIG. 14 is a plot of x-ray diffractogram for vanadium
composition particles produced by laser pyrolysis.
[0029] FIG. 15 is a plot of an x-ray diffractogram of
V.sub.2O.sub.5 produced by heat treatment of vanadium composition
particles produced by laser pyrolysis.
[0030] FIG. 16 is a plot of differential scanning calorimetry
measurements for two silver vanadium oxide samples.
[0031] FIG. 17 is a plot of two x-ray diffractograms for silver
vanadium oxide samples.
[0032] FIG. 18 is a schematic sectional view of a test cell taken
two screws of the apparatus.
[0033] FIG. 19 is a plot of voltage as a function of specific
capacity over the first discharge cycle for five batteries produced
with V.sub.2O.sub.5.
[0034] FIG. 20 is a plot of voltage as a function of specific
energy over the first discharge cycle for five batteries produced
with V.sub.2O.sub.5.
[0035] FIG. 21 is a plot of specific capacity as a function of
cycle number for five batteries produced with V.sub.2O.sub.5.
[0036] FIG. 22 is a plot of voltage as a function of time under
pulse operation with a pulse current density of 25 mA/cm.sup.2 to
1.5 V for several cells produced with silver vanadium oxides
processed under different conditions.
[0037] FIG. 23 is a plot of voltage as a function of time under
pulse operation with a pulse current density of 25 mA/cm.sup.2 to
1.5 V for several cells produced with silver vanadium oxides
processed under another set of conditions.
[0038] FIG. 24 is a plot of voltage as a function of time under
pulse operation with a pulse current density of 25 mA/cm.sup.2 to
1.5 V for two cells produced with silver vanadium oxides processed
under different mixing conditions.
[0039] FIG. 25 is a plot of voltage as a function of time under
pulse operation with a pulse current density of 25 mA/cm.sup.2 to
1.5 V for several cells produced with silver vanadium oxides
processed with different silver to vanadium ratios.
[0040] FIG. 26 is a plot of voltage as a function of time under
pulse operation with a pulse current density of 25 mA/cm.sup.2 to
1.5 V for two cells produced with silver vanadium oxides in which
the cathode materials were processed under different
conditions.
[0041] FIG. 27 is a plot of voltage as a function of time under
pulse operation with a pulse current density of 25 mA/cm.sup.2 to
1.5 V for several cells produced with silver vanadium oxides using
different electrolyte solvents.
[0042] FIG. 28 is a plot of voltage as a function of specific
capacity at a current density of 0.309 mA/cm.sup.2 to 1.0 V for the
cells of FIG. 27.
[0043] FIG. 29 is a plot of voltage as a function of time under
pulse operation with a pulse current density of 25 mA/cm.sup.2 to
1.5 V for several cells produced with silver vanadium oxides using
different electrically conductive diluents.
[0044] FIG. 30 is a plot of voltage as a function of time under
pulse operation with a pulse current density of 60 mA/cm.sup.2 to
1.5 V for two cells produced with silver vanadium oxides using
different electrically conductive diluents.
[0045] FIG. 31 is a plot of voltage as a function of cathode
thickness for silver vanadium oxide pellets.
[0046] FIG. 32 is a plot of specific capacity as a function of
cathode thickness for silver vanadium oxide pellets.
[0047] FIG. 33 is a plot of specific energy as a function of
cathode thickness for silver vanadium oxide pellets.
[0048] FIG. 34 is a plot of voltage as a function of time under
pulse operation with a pulse current density of 25 mA/cm.sup.2 to
1.5 V for eight silver vanadium oxide cells produced with different
cathode thicknesses.
[0049] FIG. 35 is a plot of voltage as a function of time under
pulse operation with a pulse current density of 70 mA/cm.sup.2 to
1.5 V for six cells produced with different cathode
thicknesses.
[0050] FIG. 36 is a plot of specific energy as a function of pulse
current density for several cathode thicknesses for silver vanadium
oxide pellets.
[0051] FIG. 37 is a plot of specific power as a function of pulse
current density for several cathode thicknesses for silver vanadium
oxide pellets.
[0052] FIG. 38 is a plot of voltage as a function of time under
pulse operation with a pulse current density of 25 mA/cm.sup.2 to
1.5 V for three silver vanadium oxide cells produced with different
cathode densities.
[0053] FIG. 39 is a plot of voltage as a function of time under
pulse operation with a pulse current density of 60 mA/cm.sup.2 to
1.5 V for three silver vanadium oxide cells produced with different
cathode densities.
[0054] FIG. 40 is a plot of specific energy as a function of rate
for pulse operation with three different cathode densities for
silver vanadium oxide pellets.
[0055] FIG. 41 is a plot of specific power as a function of rate
for pulse operation with three different cathode densities for
silver vanadium oxide pellets.
[0056] FIG. 42 is a plot of voltage as a function of time under
pulse operation with a pulse current density of 25 mA/cm.sup.2 to
1.5 V for three silver vanadium oxide cells produced with different
cathode densities and thicknesses.
[0057] FIG. 43 is a plot of voltage as a function of time under
pulse operation with a pulse current density of 70 mA/cm.sup.2 to
1.5 V for three silver vanadium oxide cells produced with different
cathode densities and thicknesses.
[0058] FIG. 44 is a plot of voltage as a function of time for
silver vanadium oxide cells under pulse operation for several
values of pulse current densities to 1.5 V.
[0059] FIG. 45 is a plot of voltage as a function of time for
silver vanadium oxide cells initially discharged under a continuous
drain to 2.6 volts followed by pulsed operation at four different
pulsed current densities to 1.5 V.
[0060] FIG. 46 is a plot of voltage as a function of time for
silver vanadium oxide cells initially discharged under a continuous
drain to 2.5 volts followed by pulsed operation at four different
pulsed current densities to 1.5 V.
[0061] FIG. 47 is a plot of an accelerated pulse test of silver
vanadium oxide cells performed under a pulse current density of 60
mA/cm.sup.2 to 1.5 V for a cell with a 100 kilo-ohm load and for a
cell with no load.
DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS
[0062] Submicron silver vanadium oxide particles are used to
produce batteries with extremely high rate capabilities. In
particular, the improved batteries have very high pulsed specific
energies and very high maximum specific powers along with very high
continuous specific capacities. In preferred embodiments, the
silver vanadium oxide has a stoichiometry of approximately
Ag.sub.2V.sub.4O.sub.11 and is free of detectable silver
metavanadate, AgVO.sub.3. In other words, the
Ag.sub.2V.sub.4O.sub.11 active form of silver vanadium oxide is
phase pure with at most insignificant traces of AgVO.sub.3.
Improved processing approaches lead both to improved metal vanadium
oxide particles, such as silver vanadium oxide particles, and to
improved battery performance. The improved batteries are
particularly suitable for employment in implantable medical
devices, especially defibrillators.
[0063] The synthesis of submicron metal vanadium oxide particles,
in particular silver vanadium oxide particles, is described in
copending and commonly assigned U.S. patent application Ser. No.
09/246,076, now U.S. Pat. No. 6,225,007 to Home et. al, entitled
"Metal Vanadium Oxide Particles" and Ser. No. 09/311,506, now U.S.
Pat. No. 6,394,494 to Reitz et al., entitled "Metal Vanadium Oxide
Particles," both of which are incorporated herein by reference.
These applications further describe the incorporation of these
particles into improved batteries, especially lithium-based
batteries. Herein, improved techniques for the synthesis of metal
vanadium oxides are described using submicron vanadium oxides as
starting materials. In addition, improved approaches for
constructing batteries from submicron metal vanadium oxide
particles are described which result in significantly improved high
rate capacity batteries.
[0064] Vanadium oxide nanoparticles with various stoichiometries
and crystal structures can be produced by laser pyrolysis alone or
with additional processing. These various forms of submicron
vanadium oxide particles, preferably submicron V.sub.2O.sub.5, can
be used as starting materials for the formation of metal vanadium
oxide nanoparticles. The multiple metal composite particles are
formed by mixing the vanadium oxide nanoparticles with a compound
of the metal to be introduced into the vanadium oxide to form a
material with both metals in the lattice. By using appropriately
selected processing conditions, submicron particles incorporating
both metals can be formed based on the submicron character of the
initial vanadium oxide particles.
[0065] Preferred collections of metal vanadium oxide particles have
an average diameter less than a micron and high uniformity with a
narrow distribution of particle diameters. To generate submicron
vanadium oxide particles from starting materials for further
processing into metal vanadium oxides, laser pyrolysis can be used
either alone or in combination with additional processing.
Specifically, laser pyrolysis has been found to be an excellent
process for efficiently producing submicron (less than about 1
micron average diameter) and nanoscale (less than about 100 nm
average diameter) vanadium oxide particles with a narrow
distribution of average particle diameters. In addition, submicron
vanadium oxide particles produced by laser pyrolysis can be
subjected to heating under mild conditions in an oxygen environment
or an inert environment to alter the crystal properties and/or the
stoichiometry of the vanadium oxide particles. Thus, a large
variety of different types of vanadium oxide particles can be
produced using these approaches.
[0066] A basic feature of successful application of laser pyrolysis
for the production of vanadium oxide particles is production of a
reactant stream containing a vanadium precursor and a radiation
absorber. A source of atomic oxygen is required. The atomic oxygen
can be bonded within the vanadium precursor and/or can be supplied
by a separate oxygen source, such as molecular oxygen. The reactant
stream is pyrolyzed by an intense light beam, such as a laser beam.
While a laser beam is a convenient energy source, other intense
light sources can be used in laser pyrolysis. Laser pyrolysis
provides for formation of phases of materials that are difficult to
form under thermodynamic equilibrium conditions. As the reactant
stream leaves the light beam, the vanadium oxide particles are
rapidly quenched. The production of vanadium oxide particles by
laser pyrolysis is described further in copending and commonly
assigned U.S. patent application Ser. No. 08/897,778, now U.S. Pat.
No. 6,106,798 to Kambe et al., entitled "Vanadium Oxide Particles,"
incorporated herein by reference.
[0067] A flameless laser pyrolysis approach has been developed for
the synthesis of vanadium oxide particles. Preferred oxygen sources
include molecules with both hydrogen and oxygen since hydrogen can
scavenge halogens from the reactant streams as HX, X being a
halogen. Water preferably is available as an oxygen source. An
infrared absorber is used to absorb the light energy to induce the
reaction of the reactant stream. A preferred vanadium precursor for
this process is vanadium oxytrichloride (vanadyl trichloride),
VOCl.sub.3. Since vanadium oxytrichloride reacts spontaneously with
water to form vanadium oxide species and HCl, the two reactants are
delivered through a dual nozzle reactant delivery system. This
flameless process is particularly convenient for the synthesis of
low energy phases of vanadium oxide, such as V.sub.2O.sub.5 and
V.sub.6O.sub.13. Amorphous V.sub.2O.sub.5 produced by this process
can be heat treated to produce crystalline, high surface area
V.sub.2O.sub.5 particles.
[0068] Because of the resulting high uniformity and narrow particle
size distribution, laser pyrolysis is a preferred approach for
producing submicron vanadium oxide for processing into metal
vanadium oxide. However, other approaches can be used to supply
submicron vanadium oxide particles for the improved production
approaches for producing metal vanadium oxides and corresponding
batteries. Suitable alternative approaches include, for example,
flame pyrolysis and thermal pyrolysis. Flame pyrolysis can be
performed with a hydrogen-oxygen flame, wherein the flame supplies
the energy to drive the pyrolysis. Such a flame pyrolysis approach
should produce similar materials as the laser pyrolysis techniques
herein, except that flame pyrolysis approaches generally do not
produce high uniformity and a narrow particle size distribution. A
suitable flame production apparatus is described in U.S. Pat. No.
5,447,708 to Helble et al., entitled "Apparatus for Producing
Nanoscale Ceramic Particles," incorporated herein by reference.
Furthermore, submicron particles can be produced with a thermal
reaction chamber such as the apparatus described in U.S. Pat. No.
4,842,832 to Inoue et al., "Ultrafine Spherical Particles of Metal
Oxide and a Method for the Production Thereof," incorporated herein
by reference.
[0069] Qualities of the vanadium oxide particles can be altered by
heat treating the initially synthesized particles. For example, the
crystallinity and/or the stoichiometry of the vanadium oxide
particles can be altered by heat treatment. In addition, starting
with nanoscale vanadium oxide particles, metal vanadium oxide
particles can be formed by a thermal process. A second metal
precursor comprises a non-vanadium transition metal that is added
to the vanadium oxide particles. Preferred second metal precursors
include compositions with copper, silver, gold or combinations
thereof.
[0070] The second metal precursor compound is mixed with a
collection of vanadium oxide particles and heated to form the
composite particles incorporating both metals. Under suitably mild
conditions, the heat processing is effective to produce the
particles while not destroying the nanoscale of the initial
vanadium oxide particles. While vanadium oxide particles with a
variety stoichiometries can be used for the synthesis of metal
vanadium oxide particles, crystalline V.sub.2O.sub.5 particles are
preferred because the crystal structure of V.sub.2O.sub.5 is
similar to the crystal structure of Ag.sub.2V.sub.4O.sub.11. In
particular, crystalline silver vanadium oxide particles can be
formed by heating crystalline V.sub.2O.sub.5 particles mixed with
silver nitrate at low temperatures between 300-400.degree. C. for
short periods of time of 1-4 hours.
[0071] In preferred embodiments, the heat treatments are performed
in a vessel with agitation of the reactants. In particular,
complete transformation of the particles into composite multimetal
composites can be obtained in a stirred vessel presumably under
more uniform conditions than can be obtained in other heating
approaches. This stirred heating approach can be used to obtain
submicron particles of Ag.sub.2V.sub.4O.sub.11 that is virtually
free (0 to 0.5 weight percent) of silver metavanadate, AgVO.sub.3.
Silver metavanadate is not electrochemically active for battery
applications, and therefore is indicative of an undesirable form of
silver vanadium oxide.
[0072] As noted above, lithium ions can intercalate into various
forms of vanadium oxide and metal vanadium oxide particles when
subjected to electric fields. To form a positive electrode, which
acts as a cathode upon discharge of the cell, the metal vanadium
oxide particles can be incorporated into a electrode with a binder
such as a polymer. The electrode preferably incorporates additional
electrically conductive particles held by a binder along with the
metal vanadium oxide particles. The electrode can be used as a
positive electrode in a lithium battery or a lithium ion battery.
Lithium based batteries formed with cathodes including submicron
metal vanadium oxides have energy densities higher than theoretical
maximum values estimated for corresponding bulk metal vanadium
oxides. In particular, metal vanadium oxides, specifically silver
vanadium oxides, have been produced with high specific capacities
and energy densities.
[0073] The batteries described herein have high rate capabilities.
To further improve these rate capabilities, it has been discovered
that superior results are obtained by mixing the metal vanadium
oxide particles in a dispersant with electrically conductive
particles and binder under shear with a homogenizer or the like.
The mixture is filtered under vacuum to remove solvents. The
remaining paste is kneaded and rolled to form a dough-like mixture.
The dough is then cut using a die with the desired area to form the
cathode pellets. In addition, improved solvents can be used in
forming the electrolyte to improve the rate capability of the
silver vanadium oxide.
[0074] For defibrillator applications, the batteries preferably
have not only high specific capacity under slow continuous drain,
but also high power capabilities when pulsed. In particular,
preferred batteries with silver vanadium oxide have maximum
specific powers greater than about 1.5 Watts/gram (W/g). The
batteries also have correspondingly high pulsed specific energies
and high pulsed specific capacities. In preferred embodiments, the
batteries have a pulsed specific energy of at least about 575 mWh/g
down to a pulsed discharge voltage of 1.5 V, when pulsed at 25
mA/cm.sup.2 current densities in groups of four pulses spaced by 15
seconds and with 30 minutes between pulse groups.
[0075] Since the improved batteries have high specific capacities
under low loads and improved pulsed capabilities, the batteries
have improved versatility in producing long lived medical devices
for implantation. In particular, implantable medical devices
capable of cardiac defibrillation generally have additional
functions, including monitoring of heart function and possibly
heart pacing. The silver vanadium oxide batteries can be used to
carry-out one or more additional functions in addition to the
defibrillating function while providing a long lived and compact
battery suitable for implantation.
[0076] A. Particle Production Using Laser Pyrolysis
[0077] As described above, laser pyrolysis is a valuable tool for
the production of submicron and nanoscale precursor particles for
further processing into submicron metal vanadium oxide particles.
The precursor vanadium oxide particles generally can include
various crystalline and/or amorphous particles that are suitable
for subsequent processing into submicron metal vanadium oxide
particles, especially silver vanadium oxide particles. In
particular, the preferred precursor particles, as described in the
examples below, are amorphous V.sub.2O.sub.5 particles.
[0078] The reaction conditions determine the qualities of the
particles produced by laser pyrolysis. The reaction conditions for
laser pyrolysis can be controlled relatively precisely in order to
produce particles with desired properties. The appropriate reaction
conditions to produce a certain type of particles generally depend
on the design of the particular apparatus. Specific conditions used
to produce vanadium oxide particles in a particular apparatus are
described below in the Examples. Furthermore, some general
observations on the relationship between reaction conditions and
the resulting particles can be made.
[0079] Increasing the light power results in increased reaction
temperatures in the reaction region as well as a faster quenching
rate. A rapid quenching rate tends to favor production of high
energy phases, which may not be obtained with processes near
thermal equilibrium. Similarly, increasing the chamber pressure
also tends to favor the production of higher energy structures.
Also, increasing the concentration of the reactant serving as the
oxygen source in the reactant stream favors the production of
particles with increased amounts of oxygen.
[0080] Reactant flow rate and velocity of the reactant gas stream
are inversely related to particle size so that increasing the
reactant gas flow rate or velocity tends to result in smaller
particle sizes. Light power also influences particle size with
increased light power favoring larger particle formation for lower
melting materials and smaller particle formation for higher melting
materials. Also, the growth dynamics of the particles have a
significant influence on the size of the resulting particles. In
other words, different forms of a product compound have a tendency
to form different size particles from other phases under relatively
similar conditions. Similarly, in multiphase regions at which
populations of particles with different compositions are formed,
each population of particles generally has its own characteristic
narrow distribution of particle sizes.
[0081] Laser pyrolysis has become the standard terminology of
reactions driven by a intense light radiation with rapid quenching
of product after leaving a narrow reaction region defined by the
light. The name, however, is a misnomer in the sense that a strong,
incoherent, but focused light beam can replace the laser. Also, the
reaction is not a pyrolysis in the sense of a thermal pyrolysis.
The laser pyrolysis reaction is not thermally driven by the
exothermic combustion of the reactants. In fact, the "laser
pyrolysis" reaction can be conducted under conditions where no
visible flame is observed from the reaction.
[0082] Laser pyrolysis has been performed generally with gas/vapor
phase reactants. Many metal precursor compounds can be delivered
into the reaction chamber as a gas. Appropriate metal precursor
compounds for gaseous delivery generally include metal compounds
with reasonable vapor pressures, i.e., vapor pressures sufficient
to get desired amounts of precursor gas/vapor into the reactant
stream. The vessel holding liquid or solid precursor compounds can
be heated to increase the vapor pressure of the metal precursor, if
desired. Solid precursors generally are heated to produce a
sufficient vapor pressure.
[0083] A carrier gas can be bubbled through a liquid precursor to
facilitate delivery of a desired amount of precursor vapor.
Similarly, a carrier gas can be passed over the solid precursor to
facilitate delivery of the precursor vapor.. Suitable vanadium
precursors for vapor delivery include, for example, VCl.sub.4,
VOCl.sub.2, V(CO).sub.6 and VOCl.sub.3. The chlorine in these
representative precursor compounds can be replaced with other
halogens, e.g., Br, I and F.
[0084] The use of exclusively gas phase reactants is somewhat
limiting with respect to the types of precursor compounds that can
be used conveniently. Thus, techniques have been developed to
introduce aerosols containing reactant precursors into laser
pyrolysis chambers. Improved aerosol delivery apparatuses for
reaction systems are described further in commonly assigned and
copending U.S. patent application Ser. No. 09/188,670, now U.S.
Pat. No. 6,193,936 to Gardner et al., entitled "Reactant Delivery
Apparatuses," filed Nov. 9, 1998, incorporated herein by
reference.
[0085] Using aerosol delivery apparatuses, solid precursor
compounds can be delivered by dissolving the compounds in a
solvent. Alternatively, powdered precursor compounds can be
dispersed in a liquid/solvent for aerosol delivery. Liquid
precursor compounds can be delivered as an aerosol from a neat
liquid, a multiple liquid dispersion or a liquid solution. Aerosol
reactants can be used to obtain a significant reactant throughput.
A solvent/dispersant can be selected to achieve desired properties
of the resulting solution/dispersion. Suitable solvents/dispersants
include water, methanol, ethanol, isopropyl alcohol, other organic
solvents and mixtures thereof. The solvent should have a desired
level of purity such that the resulting particles have a desired
purity level. Some solvents, such as isopropyl alcohol, are
significant absorbers of infrared light from a CO.sub.2 laser such
that no additional laser absorbing compound may be needed within
the reactant stream if a CO.sub.2 laser is used as a light
source.
[0086] If aerosol precursors are formed with a solvent present, the
solvent preferably is rapidly evaporated by the light beam in the
reaction chamber such that a gas phase reaction can take place.
Thus, the fundamental features of the laser pyrolysis reaction are
unchanged by the presence of an aerosol. Nevertheless, the reaction
conditions are affected by the presence of the aerosol. Below in
the Examples, conditions are described for the production of
submicron vanadium oxide particles using aerosol precursors in a
particular laser pyrolysis reaction chamber. Thus, the parameters
associated with aerosol reactant delivery can be explored further
based on the description below.
[0087] A number of suitable solid, metal precursor compounds can be
delivered as an aerosol from solution. Suitable vanadium precursors
for aerosol production include, for example, vanadyl sulfate
trihydrate (VOSO.sub.4 3H.sub.2O), ammonium metavanadate
(NH.sub.4VO.sub.3), vanadium oxide compounds (e.g., V.sub.2O.sub.5
and V.sub.2O.sub.3, which are soluble in aqueous acid), and vanadyl
dichloride (VOCl.sub.2).
[0088] The precursor compounds for aerosol delivery are dissolved
in a solution preferably with a concentration greater than about
0.5 molar. Generally, the greater the concentration of precursor in
the solution the greater the throughput of reactant through the
reaction chamber. As the concentration increases, however, the
solution can become more viscous such that the aerosol may have
droplets with larger sizes than desired. Thus, selection of
solution concentration can involve a balance of factors in the
selection of a preferred solution concentration.
[0089] Preferred secondary reactants serving as an oxygen source
include, for example, O.sub.2, CO, H.sub.2O, CO.sub.2, O.sub.3 and
mixtures thereof. Molecular oxygen can be supplied as air. The
secondary reactant compound should not react significantly with the
metal precursor prior to entering the reaction zone since this
generally would result in the formation of large particles. If the
reactants are spontaneously reactive, the vanadium precursor and
the secondary reactant can be delivered in separate nozzles into
the reaction chamber such that they are combined just prior to
reaching the light beam. If the vanadium precursor includes oxygen,
a secondary reactant may not be needed to supply oxygen.
[0090] Laser pyrolysis can be performed with a variety of optical
frequencies, using either a laser or other strong focused light
source. Preferred light sources operate in the infrared portion of
the electromagnetic spectrum. CO.sub.2 lasers are particularly
preferred sources of light. Infrared absorbers for inclusion in the
reactant stream include, for example, C.sub.2H.sub.4, isopropyl
alcohol, NH.sub.3, SF.sub.6, SiH.sub.4 and O.sub.3. O.sub.3 can act
as both an infrared absorber and as an oxygen source. The radiation
absorber, such as the infrared absorber, absorbs energy from the
radiation beam and distributes the energy to the other reactants to
drive the pyrolysis.
[0091] Preferably, the energy absorbed from the light beam
increases the temperature at a tremendous rate, many times the rate
that heat generally would be produced by exothermic reactions under
controlled condition. While the process generally involves
nonequilibrium conditions, the temperature can be described
approximately based on the energy in the absorbing region. The
laser pyrolysis process is qualitatively different from the process
in a combustion reactor where an energy source initiates a
reaction, but the reaction is driven by energy given off by an
exothermic reaction. Thus, while this light driven process is
referred to as laser pyrolysis, it is not a thermal process even
though traditional pyrolysis is a thermal process.
[0092] An inert shielding gas can be used to reduce the amount of
reactant and product molecules contacting the reactant chamber
components. Inert gases can also be introduced into the reactant
stream as a carrier gas and/or as a reaction moderator. Appropriate
inert shielding gases include, for example, Ar, He and N.sub.2.
[0093] An appropriate laser pyrolysis apparatus generally includes
a reaction chamber isolated from the ambient environment. A
reactant inlet connected to a reactant delivery apparatus produces
a reactant stream through the reaction chamber. A light beam path
intersects the reactant stream at a reaction zone. The
reactant/product stream continues after the reaction zone to an
outlet, where the reactant/product stream exits the reaction
chamber and passes into a collection apparatus. Generally, the
light source, such as a laser, is located external to the reaction
chamber, and the light beam enters the reaction chamber through an
appropriate window.
[0094] Referring to FIG. 1, a particular embodiment 100 of a laser
pyrolysis system involves a reactant delivery apparatus 102,
reaction chamber 104, shielding gas delivery apparatus 106,
collection apparatus 108 and light source 110. A first reaction
delivery apparatus described below can be used to deliver
exclusively gaseous reactants. An alternative reactant delivery
apparatus is described for delivery of one or more reactants as an
aerosol.
[0095] Referring to FIG. 2, a first embodiment 112 of reactant
delivery apparatus 102 includes a source 120 of a precursor
compound. For liquid or solid reactants, a carrier gas from one or
more carrier gas sources 122 can be introduced into precursor
source 120 to facilitate delivery of the reactant. Precursor source
120 can be a liquid holding container, a solid precursor delivery
apparatus or other suitable container. The carrier gas from carrier
gas source 122 preferably is either an infrared absorber and/or an
inert gas.
[0096] The gases from precursor source 120 are mixed with gases
from infrared absorber source 124, inert gas source 126 and/or
secondary reactant source 128 by combining the gases in a single
portion of tubing 130. The gases are combined a sufficient distance
from reaction chamber 104 such that the gases become well mixed
prior to their entrance into reaction chamber 104. The combined gas
in tube 130 passes through a duct 132 into channel 134, which is in
fluid communication with reactant inlet 206.
[0097] A second reactant can be supplied from second reactant
source 138, which can be a liquid reactant delivery apparatus, a
solid reactant delivery apparatus, a gas cylinder or other suitable
container or containers. As shown in FIG. 2, second reactant source
138 delivers a second reactant to duct 132 by way of tube 130.
Alternatively, mass flow controllers 146 can be used to regulate
the flow of gases within the reactant delivery system of FIG. 2.
The second reactant can be delivered through a second duct for
delivery into the reactant chamber through a second channel such
that the reactants do not mix until they are in the reaction
chamber.
[0098] As noted above, the reactant stream can include one or more
aerosols. The aerosols can be formed within reaction chamber 104 or
outside of reaction chamber 104 prior to injection into reaction
chamber 104. If the aerosols are produced prior to injection into
reaction chamber 104, the aerosols can be introduced through
reactant inlets comparable to those used for gaseous reactants,
such as reactant inlet 134 in FIG. 2.
[0099] Referring to FIG. 3, embodiment 210 of the reactant supply
system 102 can be used to supply an aerosol to duct 132. Reactant
supply system 210 includes an outer nozzle 212 and an inner nozzle
214. Outer nozzle 212 has an upper channel 216 that leads to a
rectangular outlet 218 at the top of outer nozzle 212, as shown in
the insert in FIG. 3. Rectangular nozzle has selected dimensions to
produce a reactant stream of desired expanse within the reaction
chamber. Outer nozzle 212 includes a drain tube 220 in base plate
222. Drain tube 220 is used to remove condensed aerosol from outer
nozzle 212. Inner nozzle 214 is secured to outer nozzle 212 at
fitting 224.
[0100] The top of the nozzle preferably is a twin orifice internal
mix atomizer 226. Liquid is fed to the atomizer through tube 228,
and gases for introduction into the reaction chamber are fed to the
atomizer through tube 230. Interaction of the gas with the liquid
assists with droplet formation.
[0101] Referring to FIG. 1, the reaction chamber 104 includes a
main chamber 250. Reactant supply system 102 connects to the main
chamber 250 at injection nozzle 252. Reaction chamber 104 can be
heated to a surface temperature above the dew point of the mixture
of reactants and inert components at the pressure in the
apparatus.
[0102] The end of injection nozzle 252 has an annular opening 254
for the passage of inert shielding gas, and a reactant inlet 256
(left lower insert) for the passage of reactants to form a reactant
stream in the reaction chamber. Reactant inlet 256 preferably is a
slit, as shown in the lower inserts of FIG. 1. Annular opening 254
has, for example, a diameter of about 1.5 inches and a width along
the radial direction from about 1/8 in to about {fraction (1/16)}
in. The flow of shielding gas through annular opening 254 helps to
prevent the spread of the reactant gases and product particles
throughout reaction chamber 104.
[0103] Tubular sections 260, 262 are located on either side of
injection nozzle 252. Tubular sections 260, 262 include ZnSe
windows 264, 266, respectively. Windows 264, 266 are about 1 inch
in diameter. Windows 264, 266 are preferably cylindrical lenses
with a focal length equal to the distance between the center of the
chamber to the surface of the lens to focus the light beam to a
point just below the center of the nozzle opening. Windows 264, 266
preferably have an antireflective coating. Appropriate ZnSe lenses
are available from Laser Power Optics, San Diego, Calif. Tubular
sections 260, 262 provide for the displacement of windows 264, 266
away from main chamber 250 such that windows 264, 266 are less
likely to be contaminated by reactants and/or products. Window 264,
266 are displaced, for example, about 3 cm from the edge of the
main chamber 250.
[0104] Windows 264, 266 are sealed with a rubber o-ring to tubular
sections 260, 262 to prevent the flow of ambient air into reaction
chamber 104. Tubular inlets 268, 270 provide for the flow of
shielding gas into tubular sections 260, 262 to reduce the
contamination of windows 264, 266. Tubular inlets 268, 270 are
connected to shielding gas delivery apparatus 106.
[0105] Referring to FIG. 1, shielding gas delivery system 106
includes inert gas source 280 connected to an inert gas duct 282.
Inert gas duct 282 flows into annular channel 284 leading to
annular opening 254. A mass flow controller 286 regulates the flow
of inert gas into inert gas duct 282. If reactant delivery system
112 of FIG. 2 is used, inert gas source 126 can also function as
the inert gas source for duct 282, if desired. Referring to FIG. 1,
inert gas source 280 or a separate inert gas source can be used to
supply inert gas to tubes 268, 270. Flow to tubes 268, 270
preferably is controlled by a mass flow controller 288.
[0106] Light source 110 is aligned to generate a light beam 300
that enters window 264 and exits window 266. Windows 264, 266
define a light path through main chamber 250 intersecting the flow
of reactants at reaction zone 302. After exiting window 266, light
beam 300 strikes power meter 304, which also acts as a beam dump.
An appropriate power meter is available from Coherent Inc., Santa
Clara, Calif. Light source 110 can be a laser or an intense
conventional light source such as an arc lamp. Preferably, light
source 110 is an infrared laser, especially a CW CO.sub.2 laser
such as an 1800 watt maximum power output laser available from PRC
Corp., Landing, N.J.
[0107] Reactants passing through reactant inlet 256 in injection
nozzle 252 initiate a reactant stream. The reactant stream passes
through reaction zone 302, where reaction involving the metal
precursor compounds takes place. Heating of the gases in reaction
zone 302 is extremely rapid, roughly on the order of 105 degree
C./sec depending on the specific conditions. The reaction is
rapidly quenched upon leaving reaction zone 302, and particles 306
are formed in the reactant/ product stream. The nonequilibrium
nature of the process allows for the production of nanoparticles
with a highly uniform size distribution and structural
homogeneity.
[0108] The path of the reactant stream continues to collection
nozzle 310. Collection nozzle 310 has a circular opening 312, as
shown in the upper insert of FIG. 1. Circular opening 312 feeds
into collection system 108.
[0109] The chamber pressure is monitored with a pressure gauge 320
attached to the main chamber. The preferred chamber pressure for
the production of the desired oxides generally ranges from about 80
Torr to about 650 Torr.
[0110] Collection system 108 preferably includes a curved channel
330 leading from collection nozzle 310. Because of the small size
of the particles, the product particles follow the flow of the gas
around curves. Collection system 108 includes a filter 332 within
the gas flow to collect the product particles. Due to curved
section 330, the filter is not supported directly above the
chamber. A variety of materials such as Teflon.RTM.
(polytetrafluoroethylene), glass fibers and the like can be used
for the filter as long as the material is inert and has a fine
enough mesh to trap the particles. Preferred materials for the
filter include, for example, a glass fiber filter from ACE Glass
Inc., Vineland, N.J. and cylindrical Nomex.RTM. filters from AF
Equipment Co., Sunnyvale, Calif.
[0111] Pump 334 is used to maintain collection system 108 at a
selected pressure. It may be desirable to flow the exhaust of the
pump through a scrubber 336 to remove any remaining reactive
chemicals before venting into the atmosphere.
[0112] The pumping rate is controlled by either a manual needle
valve or an automatic throttle valve 338 inserted between pump 334
and filter 332. As the chamber pressure increases due to the
accumulation of particles on filter 332, the manual valve or the
throttle valve can be adjusted to maintain the pumping rate and the
corresponding chamber pressure.
[0113] The apparatus is controlled by a computer 350. Generally,
the computer controls the light source and monitors the pressure in
the reaction chamber. The computer can be used to control the flow
of reactants and/or the shielding gas.
[0114] The reaction can be continued until sufficient particles are
collected on filter 332 such that pump 334 can no longer maintain
the desired pressure in the reaction chamber 104 against the
resistance through filter 332. When the pressure in reaction
chamber 104 can no longer be maintained at the desired value, the
reaction is stopped, and filter 332 is removed. With this
embodiment, about 1-300 grams of particles can be collected in a
single run before the chamber pressure can no longer be maintained.
A single run generally can last up to about 10 hours depending on
the reactant delivery system, the type of particle being produced
and the type of filter being used.
[0115] An alternative embodiment of a laser pyrolysis apparatus is
shown in FIG. 4. Laser pyrolysis apparatus 400 includes a reaction
chamber 402. The reaction chamber 402 has a shape of a rectangular
parallelapiped. Reaction chamber 402 extends with its longest
dimension along the laser beam. Reaction chamber 402 has a viewing
window 404 at its side, such that the reaction zone can be observed
during operation.
[0116] Reaction chamber 402 has tubular extensions 408, 410 that
define an optical path through the reaction chamber. Tubular
extension 408 is connected with a seal to a cylindrical lens 412.
Tube 414 connects laser 416 or other optical source with lens 412.
Similarly, Tubular extension 410 is connected with a seal to tube
418, which further leads to beam dump/light meter 420. Thus, the
entire light path from laser 416 to beam dump 420 is enclosed.
[0117] Inlet nozzle 426 connects with reaction chamber 402 at its
lower surface 428. Inlet nozzle 426 includes a plate 430 that bolts
into lower surface 428 to secure inlet nozzle 426. Referring to
sectional views in FIGS. 5 and 6, inlet nozzle 426 includes an
inner nozzle 432 and an outer nozzle 434. Inner nozzle 432
preferably has a twin orifice internal mix atomizer 436 at the top
of the nozzle. Suitable gas atomizers are available from Spraying
Systems, Wheaton, Ill. The twin orifice internal mix atomizer 436
has a fan shape to produce a thin sheet of aerosol and gaseous
precursors. Liquid is fed to the atomizer through tube 438, and
gases for introduction into the reaction chamber are fed to the
atomizer through tube 440. Interaction of the gas with the liquid
assists with droplet formation.
[0118] Outer nozzle 434 includes a chamber section 450, a funnel
section 452 and a delivery section 454. Chamber section 450 holds
the atomizer of inner nozzle 432. Funnel section 452 directs the
aerosol and gaseous precursors into delivery section 454. Delivery
section 450 leads to an about 3 inch by 0.5 inch rectangular outlet
456, shown in the insert of FIG. 5. Outer nozzle 434 includes a
drain 458 to remove any liquid that collects in the outer nozzle.
Outer nozzle 434 is covered by an outer wall 460 that forms an
shielding gas opening 462 surrounding outlet 456. Inert gas is
introduced through inlet 464.
[0119] Referring to FIG. 4, exit nozzle 470 connects to apparatus
400 at the top surface of reaction chamber 402. Exit nozzle 470
leads to filter chamber 472. Filter chamber 472 connects with pipe
474 which leads to a pump. A cylindrical filter is mounted at the
opening to pipe 474. Suitable cylindrical filters are described
above.
[0120] Another alternative design of a laser pyrolysis apparatus
has been described in U.S. Pat. No. 5,958,348 to Bi et al.,
entitled "Efficient Production of Particles by Chemical Reaction,"
incorporated herein by reference. This alternative design is
intended to facilitate production of commercial quantities of
particles by laser pyrolysis. Additional embodiments and other
appropriate features for commercial capacity laser pyrolysis
apparatuses are described in copending and commonly assigned U.S.
patent application Ser. No. 09/362,631 to Mosso et al., entitled
"Particle Production Apparatus," incorporated herein by
reference.
[0121] In one preferred embodiment of a commercial capacity laser
pyrolysis apparatus, the reaction chamber and reactant inlet are
elongated significantly along the light beam to provide for an
increase in the throughput of reactants and products. The original
design of the apparatus was based on the introduction of purely
gaseous reactants. The embodiments described above for the delivery
of aerosol reactants can be adapted for the elongated reaction
chamber design. Additional embodiments for the introduction of an
aerosol with one or more aerosol generators into an elongated
reaction chamber is described in commonly assigned and copending
U.S. patent application Ser. No. 09/188,670 now U.S. Pat. No.
6,193,936 to Gardner et al., entitled "Reactant Delivery
Apparatuses," incorporated herein by reference.
[0122] In general, the laser pyrolysis apparatus with the elongated
reaction chamber and reactant inlet is designed to reduce
contamination of the chamber walls, to increase the production
capacity and to make efficient use of resources. To accomplish
these objectives, the elongated reaction chamber provides for an
increased throughput of reactants and products without a
corresponding increase in the dead volume of the chamber. The dead
volume of the chamber can become contaminated with unreacted
compounds and/or reaction products. Furthermore, an appropriate
flow of shielding gas confines the reactants and products within a
flow stream through the reaction chamber. The high throughput of
reactants makes efficient use of the laser energy.
[0123] The improved reaction system includes a collection apparatus
to remove the nanoparticles from the reactant stream. The
collection system can be designed to collect particles in a batch
mode with the collection of a large quantity of particles prior to
terminating production. A filter or the like can be used to collect
the particles in batch mode. One embodiment suitable for batch
collection is described further below. Alternatively, the
collection system can be designed to run in a continuous production
mode by switching between different particle collectors within the
collection apparatus or by providing for removal of particles
without exposing the collection system to the ambient atmosphere. A
preferred embodiment of a collection apparatus for continuous
particle production is described in copending and commonly assigned
U.S. patent application Ser. No. 09/107,729 now U.S. Pat. No.
6,270,732 to Gardner et al., entitled "Particle Collection
Apparatus And Associated Methods," incorporated herein by
reference.
[0124] The design of the improved reaction chamber 470 is shown
schematically in FIG. 7. A reactant inlet 472 leads to main chamber
474. Reactant inlet 472 conforms generally to the shape of main
chamber 474. Main chamber 474 includes an outlet 476 along the
reactant/product stream for removal of particulate products, any
unreacted gases and inert gases. Shielding gas inlets 478 are
located on both sides of reactant inlet 472. Shielding gas inlets
are used to form a blanket of inert gases on the sides of the
reactant stream to inhibit contact between the chamber walls and
the reactants or products. The dimensions of elongated reaction
chamber 474 and reactant inlet 472 preferably are designed for high
efficiency particle production. Reasonable dimensions for reactant
inlet 472 for the production of ceramic nanoparticles, when used
with a 1800 watt CO.sub.2 laser, are from about 5 mm to about 1
meter.
[0125] Tubular sections 480, 482 extend from the main chamber 474.
Tubular sections 480, 482 hold windows 484, 486 to define a light
beam path 488 through the reaction chamber 470. Tubular sections
480, 482 can include inert gas inlets 490, 492 for the introduction
of inert gas into tubular sections 480, 482.
[0126] Referring to FIGS. 8-10, a specific embodiment of a laser
pyrolysis reaction system 500 with aerosol reactant delivery
includes reaction chamber 502, a particle collection system 504,
laser 506 and a reactant delivery system 508 (described below).
Reaction chamber 502 includes reactant inlet 514 at the bottom of
reaction chamber 502 where reactant delivery system 508 connects
with reaction chamber 502. In this embodiment, the reactants are
delivered from the bottom of the reaction chamber while the
products are collected from the top of the reaction chamber. The
configuration can be reversed with the reactants supplied from the
top and product collected from the bottom, if desired.
[0127] Shielding gas conduits 516 are located on the front and back
of reactant inlet 514. Inert gas is delivered to shielding gas
conduits 516 through ports 518. The shielding gas conduits direct
shielding gas along the walls of reaction chamber 502 to inhibit
association of reactant gases or products with the walls.
[0128] Reaction chamber 502 is elongated along one dimension
denoted in FIG. 8 by "w". A laser beam path 520 enters the reaction
chamber through a window 522 displaced along a tube 524 from the
main chamber 526 and traverses the elongated direction of reaction
chamber 502. The laser beam passes through tube 528 and exits
window 530. In one preferred embodiment, tubes 524 and 528 displace
windows 522 and 530 about 11 inches from the main chamber. The
laser beam terminates at beam dump 532. In operation, the laser
beam intersects a reactant stream generated through reactant inlet
514.
[0129] The top of main chamber 526 opens into particle collection
system 504. Particle collection system 504 includes outlet duct 534
connected to the top of main chamber 526 to receive the flow from
main chamber 526. Outlet duct 534 carries the product particles out
of the plane of the reactant stream to a cylindrical filter 536.
Filter 536 has a cap 538 on one end. The other end of filter 536 is
fastened to disc 540. Vent 542 is secured to the center of disc 540
to provide access to the center of filter 536. Vent 542 is attached
by way of ducts to a pump. Thus, product particles are trapped on
filter 536 by the flow from the reaction chamber 502 to the pump.
Suitable pumps were described above. Suitable pumps include, for
example, an air cleaner filter for a Saab 9000 automobile
(Purilator part A44-67), which is wax impregnated paper with
Plasticol or polyurethane end caps.
[0130] In one preferred embodiment, reactant delivery system 508
includes a reactant nozzle 550, as shown in FIG. 11. Reactant
nozzle 550 preferably includes an attachment plate 552. Reactant
nozzle 550 attaches at reactant inlet 514 with attachment plate 552
bolting to the bottom of main chamber 526. In one preferred
embodiment, nozzle 550 has four channels that terminate at four
slits 554, 556, 558, 560. Slits 558 and 560 can be used for the
delivery of vanadium precursors and other desired components of the
reactant stream. Slits 554, 556 can be used for the delivery of
inert shielding gas. If a secondary reactant is spontaneously
reactive with the vanadium precursor, it can be delivered also
through slits 554, 556. One apparatus used for the production of
vanadium oxide particles had dimensions for slits 554, 556, 558,
560 of 3 inches by 0.04 inches.
[0131] B. Heat Processing
[0132] 1. Vanadium Oxide Particles
[0133] Significant properties of submicron and nanoscale particles
can be modified by heat processing. Suitable starting material for
the heat treatment include particles produced by laser pyrolysis.
In addition, particles used as starting material for a heat
treatment process can have been subjected to one or more prior
heating steps under different conditions. For the heat processing
of particles formed by laser pyrolysis, the additional heat
processing can improve the crystallinity, remove contaminants, such
as elemental carbon, and/or alter the stoichiometry, for example,
by incorporation of additional oxygen or removal of oxygen.
[0134] Of particular interest, particles of vanadium oxide can be
formed by laser pyrolysis. Then, a subsequent heat treatment can be
used to convert these particles into desired forms of high quality
vanadium oxide particles. In preferred embodiments, the heat
treatment substantially maintains the submicron or nanoscale size
and size uniformity of the particles from laser pyrolysis. In other
words, particle size is not compromised by thermal processing.
[0135] The starting materials generally can be particles of any
size and shape, although submicron and nanoscale particles are
preferred starting materials. The nanoscale particles have an
average diameter of less than about 1000 nm and preferably from
about 5 nm to about 500 nm, and more preferably from about 5 nm to
about 150 nm. Suitable nanoscale starting materials have been
produced by laser pyrolysis.
[0136] The particles are heated in an oven or the like to provide
generally uniform heating. The processing conditions generally are
mild, such that significant amounts of particle sintering does not
occur. Thus, the temperature of heating preferably is low relative
to the melting point of the starting material and the product
material.
[0137] The atmosphere over the particles can be static, or gases
can be flowed through the system. The atmosphere for the heating
process can be an oxidizing atmosphere, a reducing atmosphere or an
inert atmosphere. In particular, for conversion of amorphous
particles to crystalline particles or from one crystalline
structure to a different crystalline structure of essentially the
same stoichiometry, the atmosphere generally can be inert.
[0138] Appropriate oxidizing gases include, for example, O.sub.2,
O.sub.3, CO, CO.sub.2, and combinations thereof. The O.sub.2 can be
supplied as air. Reducing gases include, for example, H.sub.2.
Oxidizing gases or reducing gases optionally can be mixed with
inert gases such as Ar, He and N.sub.2. When inert gas is mixed
with the oxidizing/ reducing gas, the gas mixture can include from
about 1 percent oxidizing/reducing gas to about 99 percent
oxidizing/reducing gas, and more preferably from about 5 percent
oxidizing/reducing gas to about 99 percent oxidizing/reducing gas.
Alternatively, either essentially pure oxidizing gas, pure reducing
gas or pure inert gas can be used, as desired. Care must be taken
with respect to the prevention of explosions when using highly
concentrated reducing gases.
[0139] The precise conditions can be altered to vary the type of
vanadium oxide particles that are produced. For example, the
temperature, time of heating, heating and cooling rates, the
surrounding gases and the exposure conditions with respect to the
gases can all be selected to produce desired product particles.
Generally, while heating under an oxidizing atmosphere, the longer
the heating period the more oxygen that is incorporated into the
material, prior to reaching equilibrium. Once equilibrium
conditions are reached, the overall conditions determine the
crystalline phase of the powders.
[0140] A variety of ovens or the like can be used to perform the
heating. An example of an apparatus 500 to perform this processing
is displayed in FIG. 12. Apparatus 600 includes a jar 602, which
can be made from glass or other inert material, into which the
particles are placed. Suitable glass reactor jars are available
from Ace Glass (Vineland, N.J.). For higher temperatures alloy jars
can be used to replace the glass jars. The top of glass jar 602 is
sealed to a glass cap 604, with a Teflon.RTM. gasket 606 between
jar 602 and cap 604. Cap 604 can be held in place with one or more
clamps. Cap 604 includes a plurality of ports 608, each with a
Teflon.RTM. bushing. A multiblade stainless steel stirrer 610
preferably is inserted through a central port 608 in cap 604.
Stirrer 610 is connected to a suitable motor.
[0141] One or more tubes 612 are inserted through ports 608 for the
delivery of gases into jar 602. Tubes 612 can be made from
stainless steel or other inert material. Diffusers 614 can be
included at the tips of tubes 612 to disburse the gas within jar
602. A heater/furnace 616 generally is placed around jar 602.
Suitable resistance heaters are available from Glas-col (Terre
Haute, Ind.). One port preferably includes a T-connection 618. The
temperature within jar 602 can be measured with a thermocouple 618
inserted through T-connection 618. T-connection 618 can be further
connected to a vent 620. Vent 620 provides for the venting of gas
circulated through jar 602. Preferably vent 620 is vented to a fume
hood or alternative ventilation equipment.
[0142] Preferably, desired gases are flowed through jar 602. Tubes
612 generally are connected to an oxidizing gas source and/or an
inert gas source. Oxidizing gas, inert gas or a combination thereof
to produce the desired atmosphere are placed within jar 602 from
the appropriate gas source(s). Various flow rates can be used. The
flow rate preferably is between about 1 standard cubic centimeters
per minute (seem) to about 1000 sccm and more preferably from about
10 sccm to about 500 sccm. The flow rate generally is constant
through the processing step, although the flow rate and the
composition of the gas can be varied systematically over time
during processing, if desired. Alternatively, a static gas
atmosphere can be used.
[0143] For the processing of vanadium oxide particle produced by
laser pyrolysis, the temperatures generally range from about
50.degree. C. to about 1200.degree. C. Preferred temperature ranges
depend on the starting material and the target product vanadium
oxide. For the processing of nanoscale VO.sub.2 into crystalline
V.sub.2O.sub.5, the temperature preferably ranges from about
400.degree. C. to about 1200.degree. C. For the processing of laser
pyrolysis produced V.sub.2O.sub.5, the temperature preferably
ranges from 300.degree. C. to about 750.degree. C. The heating
generally is continued for greater than about 5 minutes, and
typically is continued for from about 10 minutes to about 120
hours, in most circumstances from about 10 minutes to about 5
hours. Preferred heating temperatures and times will depend on the
particular starting material and target product. Some empirical
adjustment may be required to produce the conditions appropriate
for yielding a desired material. Typically, submicron and nanoscale
powders can be processed at lower temperatures while still
achieving the desired reaction. The use of mild conditions avoids
significant interparticle sintering resulting in larger particle
sizes. To prevent particle growth, the particles preferably are
heated for short periods of time at high temperatures or for longer
periods of time at lower temperatures. Some controlled sintering of
the particles can be performed at somewhat higher temperatures to
produce slightly larger, average particle diameters.
[0144] As noted above, heat treatment can be used to perform a
variety of desirable transformations for nanoparticles. For
example, the conditions to convert crystalline VO.sub.2 to
orthorhombic V.sub.2O.sub.5 and 2-D crystalline V.sub.2O.sub.5, and
amorphous V.sub.2O.sub.5 to orthorhombic V.sub.2O.sub.5 and 2-D
crystalline V.sub.2O.sub.5 are describe in U.S. Pat. No. 5,989,514,
to Bi et al., entitled "Processing of Vanadium Oxide Particles With
Heat," incorporated herein by reference. Conditions for the removal
of carbon coatings from metal oxide nanoparticles is described in
copending and commonly assigned U.S. patent application Ser. No.
09/123,255 now U.S. Pat. No. 6,387,531, entitled "Metal (Silicon)
Oxide/Carbon Composite Particles," incorporated herein by
reference. The incorporation of lithium from a lithium salt into
metal oxide nanoparticles in a heat treatment process is described
in copending and commonly assigned U.S. patent application Ser. No.
09/311,506, now U.S. Pat. No. 6,394,494 to Reitz et al., entitled
"Metal Vanadium Oxide Particles," and copending and commonly
assigned U.S. patent application Ser. No. 09/334,203 to Kumar et
al., entitled "Reaction Methods for Producing Ternary Particles,"
both of which are incorporated herein by reference.
[0145] 2. Silver Vanadium Oxide Synthesis
[0146] Heat processing has been found to be a useful approach to
form nanoscale metal vanadium oxide particles from submicron
vanadium oxide particles. In a preferred approach to the thermal
formation of metal vanadium oxide particles, vanadium oxide
submicron particles first are mixed with a non-vanadium metal
compound. The resulting mixture is heated in an oven or other
heating apparatus to form a metal vanadium oxide composite
particles. The heat processing to incorporate metal into the
vanadium oxide lattice can be performed in an oxidizing environment
or an inert environment. In either type of environment, the heating
step generally results in alteration of the oxygen to vanadium
ratio, although the oxidation state of vanadium does not
necessarily change. In addition, the heat processing can result in
an alteration of the crystal lattice and/or removal of adsorbed
compounds on the particles to improve the quality of the
particles.
[0147] The use of sufficiently mild conditions, i.e., temperatures
well below the melting point of the vanadium oxide particles,
results in metal incorporation into the vanadium oxide particles
without significantly sintering the particles into larger
particles. However, some sintering may take place, and the particle
morphology can change. The vanadium oxide particles used for the
process preferably are submicron vanadium oxide particles. It has
been discovered that metal vanadium oxide compositions can be
formed from vanadium oxides with an oxidation state of +5 or less
than +5. In particular, vanadium oxides with an oxidation states
from +2 (VO) to +5 (V.sub.2O.sub.5) can be used to form metal
vanadium oxide particles. Suitable forms of vanadium include
ammonium vanadate (NH.sub.4VO.sub.3), V.sub.2O.sub.5,
V.sub.2O.sub.4 or VO.sub.2, V.sub.2O.sub.3, V.sub.3O.sub.7,
V.sub.4O.sub.9, V.sub.6O.sub.13, V.sub.6O.sub.14, mixtures thereof,
and other vanadium oxides. However, crystalline V.sub.2O.sub.5
particles are the preferred starting materials for the formation of
Ag.sub.2V.sub.4O.sub.11 since the crystal structures are
similar.
[0148] Generally, the metal incorporated into the metal vanadium
oxide particle is any non-vanadium transition metal. Preferred
metals for incorporation into the vanadium oxide include, for
example, manganese, cobalt, lithium, nickel, sodium, iron,
potassium, magnesium, zinc, calcium, copper, silver, gold, and
combinations thereof. The most preferred metals are the coinage
metals, copper, silver, gold and combinations thereof. Suitable
silver compounds for processing with vanadium oxides include, for
example, silver nitrate (AgNO.sub.3), silver carbonate
(Ag.sub.2CO.sub.3), silver cyanide (AgCN), silver(II) oxide (AgO),
silver (I) oxide (Ag.sub.2O), silver thiocyanate (AgSCN), and
mixtures thereof. Suitable copper compounds include, for example,
cupric nitrate (Cu(NO.sub.3).sub.2). Alternatively, silver metal
powder, copper metal powder or gold metal powder can be used as
sources of the respective metals.
[0149] Appropriate oxidizing gases include, for example, O.sub.2 or
air. The reactant gas can be diluted with inert gases such as Ar,
He, N.sub.2, and mixtures thereof. Alternatively, the gas
atmosphere can be exclusively inert gas. Silver vanadium oxide
particles have been produced with either an inert atmosphere or an
oxidizing atmosphere, as described in the Examples below.
[0150] A variety of apparatuses can be used to perform the heat
processing of a sample. An embodiment of a suitable apparatus 600
is described above with respect to FIG. 12 for the heat processing
of vanadium oxides produced by laser pyrolysis. It has been
discovered that stirring at high rates produces the most uniform
product silver vanadium oxide. Specifically, the powders are
preferably stirred at rates of at least about 50 rpm, preferably at
least about 100 rpm, and more preferably from about 150 rpm to
about 200 rpm. High mixing speeds leads to a homogenous product and
removes agglomerates that can be electrochemically inactive
materials, such as Ag.sub.2O and AgVO.sub.3. The temperature and
time are also significant for incorporation of silver into the
lattice. This uniform material has improved performance
characteristics in high rate batteries.
[0151] In some preferred embodiments, a solution of the metal
compound is mixed with the vanadium oxide nanoparticles and
evaporated to dryness prior to further heating in the oven to
incorporate the metal into the vanadium oxide lattice.
Alternatively, the evaporation can be performed simultaneously with
the heating to form the metal vanadium oxide composition. For
example, silver nitrate and copper nitrate can be applied to the
vanadium oxide particles as an aqueous solution. Alternatively,
vanadium oxide particles can be mixed with a dry powder of the
metal compound or elemental metal powder, thereby avoiding the
evaporation step. A sufficient amount of the metal compound or
elemental metal powder is added to yield the desired amount of
incorporation of the metal into the vanadium oxide lattice. This
incorporation of the metal into the vanadium oxide lattice can be
checked, for example, through the use of x-ray diffractometry, as
described below.
[0152] The precise conditions including type of oxidizing gas (if
any), concentration of oxidizing gas, pressure or flow rate of gas,
temperature and processing time can be selected to produce the
desired type of product material. The temperatures generally are
mild, i.e., significantly below the melting point of the materials.
The use of mild conditions avoids interparticle sintering resulting
in larger particle sizes. Some controlled sintering of the
particles can be performed in the oven at somewhat higher
temperatures to produce slightly larger, average particle
diameters.
[0153] For the metal incorporation into vanadium oxide, the
temperature generally ranges from about 200.degree. C. to about
500.degree. C., preferably from about 200.degree. C. to about
400.degree. C., and more preferably from about 250.degree. C. to
about 375.degree. C. The particles preferably are heated for about
5 minutes to about 100 hours and preferably from about 1 hour to
about 4 hours. Some empirical adjustment may be required to produce
the conditions appropriate for yielding a desired material.
[0154] C. Properties of the Particles
[0155] A collection of particles of interest generally has an
average diameter for the primary particles of less than about 1
micron, alternatively less than about 500 run, in other embodiments
from about 2 nm to about 100 run, alternatively from about 5 nm to
about 75 nm, and in further embodiments from about 5 nm to about 50
nm. Particle diameters generally are evaluated by transmission
electron microscopy. Diameter measurements on particles with
asymmetries are based on an average of length measurements along
the principle axes of the particle.
[0156] The primary particles produced by laser pyrolysis usually
have a roughly spherical gross appearance. Specifically,
crystalline primary particles tend to exhibit growth that is
roughly equal in the three physical dimensions to give a gross
spherical appearance. Amorphous particles generally have an even
more spherical aspect. After heat treatment the particles may take
non-spherical shapes reflecting the crystal lattice. Upon closer
examination, crystalline particles generally have facets
corresponding to the underlying crystal lattice. Specifically,
V.sub.2O.sub.5 and Ag.sub.2V.sub.4O.sub.11 tend to form rods,
needles, plates or combinations thereof.
[0157] Because of their small size, the primary particles tend to
form loose agglomerates due to van der Waals and other
electromagnetic forces between nearby particles. These agglomerates
can be dispersed to a significant degree, if desired. Even though
the particles form loose agglomerates, the submicron or nanometer
scale of the primary particles is clearly observable in
transmission electron micrographs of the particles. Furthermore,
the particles can manifest unique properties due to their small
size and large surface area per weight of material. For example,
vanadium oxide nanoparticles can exhibit surprisingly high energy
densities in lithium batteries, as described in U.S. Pat. No.
5,952,125 to Bi et al., entitled "Batteries With Electroactive
Nanoparticles," incorporated herein by reference.
[0158] The primary particles preferably have a high degree of
uniformity in size. Laser pyrolysis, as described above, generally
results in particles having a very narrow range of particle
diameters. Furthermore, heat processing under suitably mild
conditions does not alter the very narrow range of particle
diameters. With aerosol delivery of reactants for laser pyrolysis,
the distribution of particle diameters is particularly sensitive to
the reaction conditions. Nevertheless, if the reaction conditions
are properly controlled, a very narrow distribution of particle
diameters can be obtained with an aerosol delivery system. As
determined from examination of transmission electron micrographs,
the primary particles generally have a distribution in sizes such
that at least about 95 percent, and preferably 99 percent, of the
primary particles have a diameter greater than about 40 percent of
the average diameter and less than about 225 percent of the average
diameter. Preferably, the primary particles have a distribution of
diameters such that at least about 95 percent, and preferably 99
percent, of the primary particles have a diameter greater than
about 45 percent of the average diameter and less than about 200
percent of the average diameter.
[0159] Furthermore, in preferred embodiments no primary particles
have an average diameter greater than about 5 times the average
diameter and preferably 4 times the average diameter, and more
preferably 3 times the average diameter. In other words, the
particle size distribution effectively does not have a tail
indicative of a small number of particles with significantly larger
sizes. This is a result of the small reaction region and
corresponding rapid quench of the particles. An effective cut off
in the tail of the size distribution indicates that there are less
than about 1 particle in 10.sup.6 have a diameter greater than a
specified cut off value above the average diameter. Narrow size
distributions, lack of a tail in the distributions can be exploited
in a variety of applications.
[0160] In addition, the submicron particles produced by the
techniques described herein generally have a very high purity
level. The particles produced by the above described methods are
expected to have a purity greater than the reactants because the
laser pyrolysis reaction and, when applicable, the crystal
formation process tends to exclude contaminants from the particle.
Furthermore, crystalline particles produced by laser pyrolysis have
a high degree of crystallinity. Similarly, the crystalline
particles produced by heat processing have a high degree of
crystallinity. Certain impurities on the surface of the particles
may be removed by heating the particles to achieve not only high
crystalline purity but high purity overall.
[0161] Vanadium oxide has an intricate phase diagram due to the
many possible oxidation states of vanadium. Vanadium is known to
exist in various oxidation states up to V.sup.+5. The energy
differences between the oxides of vanadium in the different
oxidation states is not large. Therefore, it is possible to produce
stoichiometric mixed valence compounds. Known forms of vanadium
oxide include, for example, VO, VO.sub.1.27, V.sub.2O.sub.3,
V.sub.3O.sub.5, VO.sub.2, V.sub.6O.sub.13, V.sub.4O.sub.9,
V.sub.3O.sub.7, and V.sub.2O.sub.5. Laser pyrolysis alone or with
additional heating can successfully yield single phase vanadium
oxide in many different oxidation states, as evidenced by x-ray
diffraction studies. These single phase materials are generally
crystalline, although some amorphous nanoparticles have been
produced. The heat treatment approaches are useful for increasing
the oxidation state of vanadium oxide particles or for converting
vanadium oxide particles to more ordered phases.
[0162] There are also mixed phase regions of the vanadium oxide
phase diagram. In the mixed phase regions, particles can be formed
that have domains with different oxidation states, or different
particles can be simultaneously formed with vanadium in different
oxidation states. In other words, certain particles or portions of
particles have one stoichiometry while other particles or portions
of particles have a different stoichiometry. Mixed phase
nanoparticles have been formed. Non-stoichiometric materials also
can be formed.
[0163] The vanadium oxides generally form crystals with octahedral
or distorted octahedral coordination. Specifically, VO,
V.sub.2O.sub.3, VO.sub.2, V.sub.6O.sub.13 and V.sub.3O.sub.7 can
form crystals with octahedral coordination. In addition,
V.sub.3O.sub.7 can form crystals with trigonal bipyramidal
coordination. V.sub.2O.sub.5 forms crystals with square pyramidal
crystal structure. V.sub.2O.sub.5 recently also has been produced
in a two dimensional crystal structure. See, M. Hibino, et al.,
Solid State Ionics 79:239-244 (1995), incorporated herein by
reference. When produced under appropriate conditions, the vanadium
oxide nanoparticles can be amorphous. The crystalline lattice of
the vanadium oxide can be evaluated using x-ray diffraction
measurements.
[0164] Metal vanadium oxide compounds can be formed with various
stoichiometries. U.S. Pat. No. 4,310,609 to Liang et al., entitled
"Metal Oxide Composite Cathode Material for High Energy Density
Batteries," incorporated herein by reference, describes the
formation of Ag.sub.0.7V.sub.2O.sub.5.5, AgV.sub.2O.sub.5.5, and
Cu.sub.0.7V.sub.2O.sub.5.5. The production of oxygen deficient
silver vanadium oxide, Ag.sub.0.7V.sub.2O.sub.5, is described in
U.S. Pat. No. 5,389,472 to Takeuchi et al., entitled "Preparation
of Silver Vanadium Oxide Cathodes Using Ag(O) and V.sub.2O.sub.5 as
Starting Materials," incorporated herein by reference. The phase
diagram of silver vanadium oxides of the formula
Ag.sub.xV.sub.2O.sub.y, 0.3.ltoreq.x.ltoreq.2.0,
4.5.ltoreq.y.ltoreq.6.0, involving stoichiometric admixtures of
V.sub.2O.sub.5 and AgVO.sub.3, are described in published European
Patent Application 0 689 256A, entitled "Cathode material for
nonaqueous electrochemical cells," incorporated herein by
reference.
[0165] D. Batteries
[0166] Referring to FIG. 13, battery 650 has a negative electrode
652, a positive electrode 654 and separator 656 between negative
electrode 652 and positive electrode 654. A single battery can
include multiple positive electrodes and/or multiple negative
electrodes. Electrolyte can be supplied in a variety of ways as
described further below. Battery 650 preferably includes current
collectors 658, 660 associated with negative electrode 652 and
positive electrode 654, respectively. Multiple current collectors
can be associated with each electrode if desired.
[0167] Lithium has been extensively used in primary and secondary
batteries. An attractive feature of metallic lithium is that it is
the most electropositive metal. Certain forms of metal, metal
oxides and mixed metal oxides are known to incorporate lithium ions
into its structure through intercalation or similar mechanisms such
as topochemical absorption. Intercalation of lithium ions can take
place in suitable forms of a vanadium oxide lattices as well as the
lattice of metal vanadium oxide compositions. Suitable metal
vanadium oxide nanoparticles for incorporation into batteries can
be produced by thermal processing of vanadium oxide nanoparticles
with a metal compound or by direct laser pyrolysis synthesis of
metal vanadium oxide nanoparticles with or without additional heat
processing.
[0168] In particular, lithium intercalates into the vanadium oxide
lattice or metal vanadium oxide lattice during discharge of the
battery. The lithium leaves the lattice upon recharging, i.e., when
a voltage is applied to the cell such that electric current flows
into the positive electrode due to the application of an external
EMF to the battery. Positive electrode 654 acts as a cathode during
discharge, and negative electrode 652 acts as an anode during
discharge of the cell. Metal vanadium oxide particles can be used
directly in a positive electrode for a lithium based battery to
provide a cell with a high energy density. Appropriate metal
vanadium oxide particles can be an effective electroactive material
for a positive electrode in either a lithium or lithium ion
battery.
[0169] Positive electrode 654 includes electroactive nanoparticles,
metal vanadium oxide particles held together with a binder such as
a polymeric binder. Particles for use in positive electrode 654
generally can have any shape, e.g., roughly spherical particles or
elongated particles, such as plate shaped, needle shaped or oblong
shaped particles. Vanadium oxide nanoparticles are know to exhibit
surprisingly high energy densities, as described in U.S. Pat. No.
5,952,125, entitled "Batteries With Electroactive Nanoparticles,"
incorporated herein by reference. The production of manganese oxide
nanoparticles is described in copending and commonly assigned U.S.
patent application Ser. No. 09/188,770 to Kumar et al. filed on
Nov. 9, 1998, entitled "Metal Oxide Particles," incorporated herein
by reference.
[0170] While some electroactive materials are reasonable electrical
conductors, a positive electrode generally includes electrically
conductive particles in addition to the electroactive
nanoparticles. These supplementary, electrically conductive
particles generally are also held by the binder. Suitable
electrically conductive particles include conductive carbon
particles such as carbon black, metal particles such as silver
particles, metal fibers such as stainless steel fibers, and the
like.
[0171] High loadings of particles can be achieved in the binder.
Particles preferably make up greater than about 80 percent by
weight of the positive electrode, and more preferably greater than
about 90 percent by weight. The binder can be any of various
suitable polymers such as polyvinylidene fluoride, polyethylene
oxide, polyethylene, polypropylene, polytetrafluoro ethylene,
polyacrylates, ethylene-(propylene-diene monomer) copolymer (EPDM)
and mixtures and copolymers thereof.
[0172] It has been discovered that the processing to produce the
electrode can be effective to improve the rate performance of the
resulting battery. Previous approaches for the production of
cathodes incorporating silver vanadium oxides have involved the
mixing together of the silver vanadium oxide powders, the
electrically conductive powders and the polymer and subsequent
pressing of the materials at high pressure to form a cathode.
Improved rate behavior was obtained, as described below in the
examples, by blending silver vanadium oxide powder, the
electrically conductive powder, a polymer binder and a solvent to
form a mixture. Sufficient solvent is added to provide for blending
of the mixture. The mixture is mixed in a homogenizer or the like.
An example of a suitable homogenizer is a T25 Basic Ultra-TURRAX
Laboratory Dispenser/Homogenizer from IKA Works, available from VWR
Scientific, San Francisco, Calif. Homogenizers are known in the art
to operate at low shear compared with other mixing approaches.
Under low shear mixing using a homogenizer, it has been observed
that better dispersion of the particles is obtained. Preferably,
the mixture is blended at high speeds for about 1 minute to about
20 minutes, preferably for about 2 minutes to about 10 minutes, and
even more preferably from about 2 minutes to about 5 minutes. Low
shear homogenizing can be conducted at greater than about 5000 rpm,
and generally at about 8000 rpm to about 24,000 rpm, which
correspond to low settings on standard homogenizers. Homogenizing
at higher rpm would be expected to yield similar results. Mixing in
the homogenizer provides an extremely well dispersed blend of the
components. Following mixing in the homogenizer, the mixture is
filtered, kneaded and rolled into a cathode sheet. The cathode is
cut into a desired shape and then dried to removed the solvent. The
drying can be performed in an oven, preferably a vacuum oven. After
drying, the cathode is pressed, preferably under pressures of about
3 to about 3.5 tons per cm.sub.2. Following pressing of the cathode
material, the cathode is preferably stored in a dry
environment.
[0173] In the case of lithium batteries, the negative electrode can
include lithium metal or lithium alloy metal either in the form of
a foil, grid or metal particles in a binder. Lithium ion batteries
use particles of a composition that can intercalate lithium. The
particles are held with a binder in the negative electrode.
Suitable intercalation compounds include, for example, graphite,
synthetic graphite, coke, mesocarbons, doped carbons, fullerenes,
tin alloys, SnO.sub.2 and mixtures and composites thereof.
[0174] Current collectors 658, 660 facilitate flow of electricity
from battery 650. Current collectors 658, 460 are electrically
conductive and generally made of metal such as nickel, stainless
steel, aluminum and copper and can be metal foil or preferably a
metal grid. Current collector 658, 660 can be on the surface of
their associated electrode or embedded within their associated
electrode.
[0175] Separator element 656 is electrically insulating and
provides for passage of ions. Ionic transmission through the
separator provides for electrical neutrality throughout the cell.
The separator prevents electroactive compounds in the positive
electrode from contacting electroactive compounds in the negative
electrode, which would result in a short circuit.
[0176] A variety of materials can be used for the separator. For
example, the separator can be formed from glass fibers that form a
porous matrix. Preferred separators are formed from polymers such
polyethylene and polypropylene. Suitable commercial polymer
separators include Celgard from Hoechst Celanese, Charlotte, N.C.
Polymer separators are porous to provide for ionic conduction.
Alternatively, polymer separators can be solid electrolytes formed
from polymers such as polyethylene oxide. Solid electrolytes
incorporate electrolyte into the polymer matrix to provide for
ionic conduction with or without the need for liquid solvent.
[0177] Electrolytes for lithium batteries or lithium ion batteries
can include any of a variety of lithium salts. Preferred lithium
salts have chemically inert anions. Suitable lithium salts include,
for example, lithium hexafluorophosphate, lithium
hexafluoroarsenate, lithium bis(trifluoromethyl sulfonyl imide),
lithium trifluoromethane sulfonate, lithium tris(trifluoromethyl
sulfonyl) methide, lithium tetrafluoroborate, lithium perchlorate,
lithium tetrachloroaluminate, lithium chloride and combinations
thereof.
[0178] If a liquid solvent is used to dissolve the electrolyte, the
solvent preferably is inert and does not dissolve the electroactive
materials. Generally appropriate solvents include, for example,
propylene carbonate, dimethyl carbonate, diethyl carbonate,
2-methyl tetrahydrofuran, dioxolane, tetrahydrofuran, methyl ethyl
carbonate, dipropyl carbonate, ethylene carbonate,
.gamma.-butyrolactone, dimethyl sulfoxide, acetonitrile, formamide,
dimethyl formamide, triglyme (tri(ethylene glycol) dimethyl ether),
diglyme (diethylene glycol dimethyl ether), DME (glyme or
1,2-dimethoxyethane or ethylene glycol dimethyl ether),
nitromethane and mixtures thereof.
[0179] Preferred embodiments involve the production of high rate
batteries. Improved rate performance has been found with the use of
highly ion conductive solvents for forming the electrolytes.
Particularly preferred solvents include a mixture of DME with
another solvent, in particular an alkylene carbonate. For example,
one preferred mixture is a approximate 1:1 volume ratio of DME and
ethylene carbonate or propylene carbonate. Generally, preferred
solvents include from about 25 volume percent DME to about 75
percent DME and more preferably from about 33 volume percent to
about 66 volume percent DME with the remainder being an alkylene
carbonate.
[0180] The shape of the battery components can be adjusted to be
suitable for the desired final product, for example, a coin cell, a
rectangular construction or a cylindrical battery. The battery
generally includes a casing with appropriate portions in electrical
contact with current collectors and/or electrodes of the battery.
If a liquid electrolyte is used, the casing should prevent the
leakage of the electrolyte. The casing can help to maintain the
battery elements in close proximity to each other to reduce
resistance within the battery. A plurality of battery cells can be
placed in a single case with the cells connected either in series
or in parallel.
[0181] During the discharge of the silver vanadium oxide battery,
lithium ions are inserted into the cathode host matrix. Over a
first voltage plateau discharging down to about 2.6 volts, silver
ions are reduced to silver metal and are expelled from the system.
Also, over the first plateau, vanadium is reduced from V.sup.+5 to
V.sup.+4. Over a second voltage plateau, vanadium is reduced from
V.sup.+4 to V.sup.+3. Lithium insertion over the second plateau is
effectively an insertion into lithium vanadium oxide since the
silver has been reduced and expelled. At the end of the first
plateau, the electrical resistance decreases relative to the
initial resistance because of the production of silver metal. Then,
the electrical resistance increases because of further lithium
intercalation into Li.sub.xV.sub.yO.sub.z. This increase in
resistance results in a voltage drop, often termed a voltage delay,
at the beginning of the second voltage plateau starting at about
2.6 volts under pulse conditions.
[0182] Voltage delay also is a function of additional anode and
cathode effects. With respect to the anode, most metals form a
protective layer on the surface that blocks access to the surface
of the metal. Electrolytes with organic solvents and lithium salts
are reduced to low potentials to form lithium salts on the surface
of the metal, i.e., a passivating layer. As the layer becomes
thicker, it takes longer to penetrate the layer and the voltage
drop is greater. In addition to a shortage of suitable electrically
conductive material in the cathode, Li.sup.+-Li.sup.+ interactions
contribute to the cathode becoming more electrically resistive,
therefore, causing the steep drop in voltage at the second
plateau.
[0183] In addition, while not wanting to be limited on theory,
nanoscale silver vanadium oxide has desirable properties regarding
rate properties. The nanoscale silver vanadium oxide particles
allow the intercalation of lithium with shorter diffusion times.
Large particle silver vanadium oxide is rate limited due to longer
diffusion times of the lithium into the Li.sub.xV.sub.yO.sub.z
composition. Shorter diffusion times in the nanoscale particles
lead to reduced Li.sup.+-Li.sup.+ repulsions. Also, the path to
insert lithium ions into the host Li.sub.xV.sub.yO.sub.z lattice is
much more tortuous in large micron size or larger particles than in
submicron or nanoscale particles.
[0184] Besides the use of preferred nanoscale silver vanadium
oxide, voltage delay can be reduced or avoided by including a
higher percentage of electrochemically inert, electrically
conductive particles, such as graphite or silver particles. While
the inclusion of conductive particles can avoid a voltage drop,
total capacity is lost. However, by using particles with improved
specific capacity, it is possible to use additional electrically
conductive particles without decreasing the capacity below desired
values. In preferred embodiments, there are at least 8 weight
percent inert electrically conductive particles in the cathode,
preferably at least about 10 weight percent, more preferably at
least about 15 weight percent and even more preferably at least
about 20 weight percent inert electrically conductive particles in
the cathode.
[0185] The high rate capable batteries described herein are
especially useful in the production of medical devices, in
particular defibrillators. Defibrillators provide pulses of
electricity to a patient's heart to induce regular beating. Lithium
batteries incorporating silver vanadium oxide have found important
commercial use in the production of implantable defibrillators. For
use in defibrillators, the battery cells deliver high current
pulses in rapid succession.
[0186] In order to test the batteries for their performance in
defibrillators, it is desirable to test the batteries in pulse
operation. A convenient pulse sequence for the battery discharge is
a pulse train with a series of four pulses every 30 minutes. Each
series of pulses includes four-10 second-25 mA/cm.sup.2 pulses
spaced 15 seconds apart. Using this pulse pattern, the battery is
drained to a voltage of 1.5 V. Using this pulse pattern, preferred
batteries have a pulsed specific capacity of at least 275 mAh/g,
preferably at least about 285 mAh/g, more preferably at least about
300 mAh/g and even more preferably at least about 320 mAH/g. At
higher current densities of 50 mA/cm.sup.2, 60 mA/cm.sup.2, 70
mA/cm.sup.2, 80 mA/cm.sup.2 and 90 mA/cm.sup.2, the total specific
capacity decreases slightly as the current densities increases.
Similarly, the batteries preferably have a pulsed specific energy
of at least about 575 mWh/g, more preferably at least about 600
mWh/g, even more preferably at least about 625 mWh/g, and even more
preferably at least about 640 mWh/g. The high rate capabilities of
the batteries described herein are also reflected in maximum
specific powers. In some embodiments, the batteries can have a
maximum specific power of at least about 1.5 W/g and,
alternatively, at least about 2.1 W/g. The specific power depends
on the rate with higher rates yielding more power since the current
is higher.
[0187] Defibrillators generally have other functions. For example,
an implantable defibrillator has a monitoring function such that it
can sense when a patient's heart undergoes fibrillation. In
addition, combination pace makers and defibrillators can be
constructed. Combination implantable devices can include a separate
battery, such as a lithium iodide battery or carbon monofluoride
battery, to perform the ongoing pacing operations such that the
high rate silver vanadium oxide battery could be reserved for
pulsed operation without depleting the battery.
[0188] Using preferred high rate batteries described herein, the
batteries also have high capacities under low amperage drain. Thus,
these batteries can be used effectively for other functions, such
as the monitoring function or a pacing function, without impairing
the defibrillating function. The silver vanadium oxide can replace
other batteries used for these other functions. In particular, it
is desirable to use a silver vanadium oxide battery for both
monitoring functions and pulse defibrillating operation.
[0189] In preferred embodiments, the silver vanadium oxides
batteries in low amperage operation exhibit an specific capacity
greater than about 340 milliampere hours per gram have been
produced. Preferred silver vanadium oxide particles exhibit an
specific capacity upon discharge to 2 volts greater than about 275
milliampere hours per gram, and preferably greater than about 280
milliampere hours per gram. Similarly, preferred silver vanadium
oxide particles exhibit an energy density upon discharge to 1.5
volts greater than about 315 milliampere hours per gram, and
preferably greater than about 325 milliampere hours per gram. In
addition, preferred silver vanadium oxide particles exhibit an
energy density upon discharge to 1.0 volts greater than about 360
milliampere hours per gram, and preferably greater than about 370
milliampere hours per gram. As described in the examples below,
specific capacities up to about 425 mAh/g upon discharge to 1 volt
have been achieved with thinner electrodes.
EXAMPLES
Example 1
Laser Pyrolysis Synthesis of Vanadium Oxide and Vanadium Carbide
Particles
[0190] Crystalline VO.sub.2, amorphous V.sub.2O.sub.5,
V.sub.8C.sub.7 particles were produced by laser pyrolysis. The
reaction was carried out in a chamber comparable to the chamber
shown in FIGS. 8-11. The VOCl.sub.3 (Strem Chemical, Inc.,
Newburyport, Mass.) precursor vapor was carried into the reaction
chamber by bubbling Ar gas through the VOCl.sub.3 liquid stored in
a container at 40.degree. C., or for higher production rate runs up
to 400 g/h by a flash vaporizer (ATMI-ADCS) at 175.degree. C. with
Argon carrier gas flowing. The reactant gas mixture containing
VOCl.sub.3, nitrogen and C.sub.2H.sub.4 was introduced into the
reactant gas nozzle for injection into the reactant chamber.
C.sub.2H.sub.4 gas was used as a laser absorbing gas. Nitrogen was
used as an inert gas to moderate the reaction.
[0191] For the production of vanadium oxides, some reactions were
performed with water as the oxygen source (secondary reactant) and
other reactions were carried out with O.sub.2 as the oxygen source.
For runs using O.sub.2 as the secondary reactant, O.sub.2 was
introduced with the VOCl.sub.3, N.sub.2 and C.sub.2H.sub.4
compounds through the central two slits of the nozzle in FIG. 11.
For runs using H.sub.2O as the secondary reactant, H.sub.2O was
introduced along with N.sub.2 in the outer two slits of the nozzle
in FIG. 11 while VOCl.sub.3, N.sub.2 and C.sub.2H.sub.4 were
introduced through the central two slits such that the VOCl.sub.3
and H.sub.2O were not mixed until they were within the reaction
zone.
[0192] Representative reaction conditions for the production of
vanadium oxide particles and vanadium carbide particles are
described in Table 1.
1 TABLE 1 Phase V.sub.8C.sub.7 VO.sub.2 V.sub.2O.sub.5 BET Surface
Area 81 45 18 Pressure (Torr) 150 150 150 N.sub.2-Win (slm) 10 10
10 N.sub.2-Sld. (slm) 2.5 2.5 2.5 Ethylene (slm) 2.5 2.5 2.5
Carrier Gas-N.sub.2 (slm) 1.4 1.4 1.4 Water (g/min.) 0 0 0.3-1.2
Oxygen (slm) 1.84 0.67 0 Laser Power-Input 780 780 780 (watts) sccm
= standard cubic centimeters per minute slm = standard liters per
minute Argon-Win. = argon flow through inlets 490, 492 Argon-Sld. =
argon flow through slots 554, 556
[0193] An x-ray diffractogram of product nanoparticles produced
under the conditions in Table 1 are shown in FIG. 14. The amorphous
V.sub.2O.sub.5 could be identified based on an amorphous profile
expected for V.sub.2O.sub.5, an elemental analysis and a
characteristic greenish-yellow color. Process conditions were
systematically changed to identify conditions where phase pure
vanadium compounds are synthesized in the reaction. In particular,
VO.sub.2, V.sub.2O.sub.3, V.sub.8C.sub.7, V.sub.6O.sub.13,
V.sub.3O.sub.7, and V.sub.2O.sub.5 were produced using the reaction
system described in this example. To produce V.sub.2O.sub.3 rather
than VO.sub.2, higher ethylene flows were used with comparable
ethylene to O.sub.2 ratios. The carbide V.sub.8C.sub.7 was produced
by decreasing the ethylene to O.sub.2 ratio values from 1 to 1.5,
as long as the ethylene flow rate was not too high. The ethylene to
vanadium ration is also significant. At higher ethylene flow rates
V.sub.2O.sub.3 is formed. Evidently, at ethylene to O.sub.2 ratio
values from 1 to 1.5 and ethylene flow rates that are not too high,
less H.sub.2 is formed. H.sub.2 can strip Cl from the vanadium
precursor to form VO which leads to vanadium oxide production.
V.sub.2O.sub.5 and V.sub.6O.sub.13 are lower temperature phases
that were produced with water as the oxygen source. With water as
the oxygen source, higher laser powers (600-800W) results in a
majority V.sub.6O.sub.13 with small amounts of VO.sub.2, and lower
laser powers (400-600W) results in amorphous V.sub.2O.sub.5.
Example 2
Heat Treatment of Vanadium Oxide Particles
[0194] The starting materials for the heat treatment were vanadium
oxide or vanadium carbide particles produced under the conditions
described in Table 1. Following heat treatment all of the particles
were converted to submicron crystalline V.sub.2O.sub.5.
[0195] The nanoparticles were heat treated at in a stirred oven
roughly as shown in FIG. 12. The particles were fed in batches of
about 80 grams into the glass jar. Oxygen was fed through a 1/8"
stainless steel tube at an oxygen flow rate of 155 cc/min. A mixing
speed of 150-200 rpm was used to constantly mix the powders during
the heat treatment. Except for the amorphous V.sub.2O.sub.5
powders, the powders were heated for 4 hours to 16 hours at
350-400.degree. C. The amorphous V.sub.2O.sub.5 powders were only
heated for 30 minutes to 2 hours to convert them to crystalline
V.sub.2O.sub.5. A heating rate of 4.degree. C./minute was used to
heat the samples to the target temperatures.
[0196] The resulting nanoparticles were single phase crystalline
V.sub.2O.sub.5 particles. A representative x-ray diffractogram of
these materials is shown in FIG. 15. The top diffractogram was
produced using commercial V.sub.2O.sub.5. The second, third and
fourth from the top were produced with crystalline V.sub.2O.sub.5
made by heat treating amorphous V.sub.2O.sub.5, VO.sub.2 and
V.sub.8C.sub.7, respectively. The bottom diffractogram was
generated using crystalline V.sub.2O.sub.5 produced from some
initial samples of vanadium oxides produced with the apparatus in
Example 1. From the x-ray diffractogram, it could be determined
that the resulting particles were orthorhombic V.sub.2O.sub.5.
[0197] Transmission electron microscopy (TEM) photographs were
obtained of representative nanoparticles following heat treatment.
The morphology of the V.sub.2O.sub.5 particles produced from
V.sub.8C.sub.7 included a mixture of rods, needles and plates. The
morphology of the particles produced from VO.sub.2 was a mixture of
rods and plates. The morphology of the particles produced from
V.sub.2O.sub.5 was plates with a b c. For all three materials, the
particles had an average diameter significantly less than about 500
nm and generally on the order of 250 nm or less. The asymmetric
particles had an average for the longer dimensions alone on the
order of 500 nm, although the averages for the smaller dimensions
alone generally were on the order of 100 nm of less. Thus, the
character of the starting material significantly effected the
morphology of the resulting V.sub.2O.sub.5 particles when produced
under mild heating conditions.
Example 3
Production of Silver Vanadium Oxide Particles From Crystalline
Particles
[0198] This example demonstrates the production of submicron silver
vanadium oxide using vanadium oxide particles as starting material.
The silver vanadium oxide is produced by heat processing. Silver
vanadium oxide particles were produced from the crystalline
V.sub.2O.sub.5 particles of Example 2 produced from VO.sub.2 of
Example 1. Silver vanadium oxide was also produced from crystalline
V.sub.2O.sub.5 produced from amorphous V.sub.2O.sub.5. This silver
vanadium oxide yielded comparable improved battery results to those
described in this example.
[0199] For each sample, about 50 g of silver nitrate (AgNO.sub.3)
(EM Industries, Hawthorne, N.Y.) was mixed with about 50 g of
V.sub.2O.sub.5 nanoparticles produced as described in Example 2.
The resulting mixture was mixed an automatic mortar & pestle
for 5-7 minutes. Then, the samples of the mixed powder were placed
separately into the stirred oven shown in FIG. 12. Oxygen gas was
flowed through the tube at flow rate of 100 standard cubic
centimeters per minute (sccm). A mixing speed of 150-200 rpm was
used to constantly mix the powders during the heat treatment. The
samples were heated at approximately the rate of 5.degree. C./min.
and cooled at the rate of approximately 5.degree. C./min. The
samples were heated at 350-400.degree. C. for 2 to 4 hours.
[0200] For comparison, some silver vanadium oxide was produced in a
tube furnace. About 4 grams of the mixed vanadium oxide and silver
nitrate was placed in a 21/4 inch boat inside a tube furnace.
O.sub.2 was flowed through the tube at a rate of 120 sccm. The
heating rate was 20.degree. C. per minute. The samples were again
heated for 350 to 400.degree. C. for two to four hours.
[0201] The structure of the particles following heating was
examined by x-ray diffraction using the Cu(K.alpha.) radiation line
on a Rigaku Miniflex x-ray diffractometer and differential scanning
calorimetry (DSC) using a model Universal V2.3C DSC apparatus from
TA Instruments, Inc., New Castle, Del. The DSC plot for the tube
furnace heat treatment indicates incomplete conversion to silver
vanadium oxide. The DSC plot for the stirred vessel silver vanadium
oxide shows only two isotherms, corresponding to a peritectic
transformation at about 558.degree. and a eutectic point at about
545.degree.. These transitions in silver vanadium oxide
Ag.sub.2V.sub.4O.sub.11 are described further in P. Fleury, Rev.
Chim. Miner., 6(5) 819 (1969). A comparison of the DSC scans for
the tube furnace heat treated sample and the stirred vessel sample
are shown in FIG. 16. The samples heated in the tube furnace have a
peak at about 460.degree. C. indicative of silver metavanadate.
[0202] The representative x-ray diffractograms for the silver
vanadium oxide samples produced in the stirred vessel (A) and the
tube furnace (B) are shown in FIG. 17. All of the heated samples
produce diffractograms with peaks indicating the presence of
Ag.sub.2V.sub.4O.sub.11. The diffractograms indicate a single phase
material since the amount of AgVO.sub.3 is so small that it is not
detectable by x-ray diffraction.
Battery Examples
[0203] To produce a test cell incorporating vanadium oxide powders
or silver vanadium oxide powders produced according to one of the
Examples above, the powders were incorporated into a cathode
structure. A desired quantity of silver vanadium oxide particles
was weighed and combined with predetermined amounts of graphite
powder (Chuetsu Graphite Works, CO., Osaka, Japan) and acetylene
black powder (Catalog number 55, Chevron Corp.) as conductive
diluents, and a 60% by weight dispersion of Teflon.RTM. (Catalog
No. 44,509-6, Aldrich Chemical Co., Milwaukee, Wis.) in water as a
binder. The graphite preferably has a BET surface area of at least
50 m.sup.2/g, preferably at least about 100 m.sup.2/g, more
preferably at least about 150 m.sup.2/g and even more preferably at
least about 200 m.sup.2/g. The acetylene black is preferably over
55 percent compressed and more preferably is 100 percent
compressed. For processing, isopropyl alcohol was added as a
dispersant to allow mixing of the components. Enough isopropyl
alcohol was added to cover the solids. In some examples described
below, graphite powder was replaced by silver nanoparticles
produced as described in copending and commonly assigned U.S.
patent application Ser. No. 09/311,506, now U.S. Pat. No. 6,394,494
to Reitz et al., entitled "Metal Vanadium Oxide Particles,"
incorporated herein by reference. The silver vanadium oxide cathode
composition following drying included 70% by weight silver vanadium
oxide nanoparticles, 10% by weight graphite, 10% by weight
acetylene black, and 10% by weight Teflon.RTM..
[0204] Cells were also produced similarly with vanadium oxide
particles except using polyvinylidene fluoride (PVDF) as the
binder. A 10 percent PVDF solution included PVDF (type 714, Elf
Atochem North America, Inc., Philadelphia, Pa.) dissolved in
1-methyl-2-pyrroidinone (Aldrich Chemical Co., Milwaukee, Wis.).
The vanadium oxide cathode composition following drying included
80% by weight silver vanadium oxide nanoparticles, 5% by weight
graphite, 5% by weight acetylene black, and 10% by weight PVDF.
[0205] The resulting combination of electro-active powders,
electrically conductive powders, binder and liquid was mixed well
in a homogenizer, T25 Basic ULTRA-TURRAX Laboratory
Dispenser/Homogenizer (number 27950-01), from IKA Works, using a
coarse 18 mm diameter dispersing tool (number 0593400). The
homogenizer was operated for about 5 minutes. Some processing was
performed for comparison in a blender rather than in the
homogenizer, as described further below. The blender was a WARING
Blender Model 34BL97 with a stainless steel mini-container, model
MC-2. The examples below demonstrate that low shear mixing in a
homogenizer disperses the small particles in the composition better
than high shear mixing in a blender.
[0206] After homogenizing, the mixture was filtered, kneaded and
rolled into a sheet with a selected thickness. An approximately
two-square centimeter area disk was cut from the sheet. The disk
was then dried and pressed in a 1.6 cm diameter die set at 12,000
pounds for 45-60 seconds to form a dense pellet. The pressed pellet
was vacuum dried and weighed. Unless otherwise specified, the dried
thickness was 0.46-0.5 mm.
Vanadium Oxide Battery Examples
[0207] The cathodes formed from the vanadium oxide powders were
formed into cells for testing. The vanadium oxide samples were
tested in a cell 700 with an airtight two-electrode configuration
shown in FIG. 18. The casing 702 for the sample battery was
obtained from Hohsen Co., Osaka, Japan. The casing included a top
portion 704 and a bottom portion 706, which are secured with four
screws 708. The two other screws not shown in FIG. 18 are behind
the two screws shown. Lithium metal (Alfa/Aesar, Ward Hill, Mass.)
was used as a negative electrode 712. Negative electrode 712 was
placed within the bottom portion 706. A separator 714, Celgard.RTM.
2400 (Hoechst Celanese, Charlotte, N.C.), was placed above the
lithium metal. A Teflon.RTM. ring 716 was placed above separator
714. A positive electrode 718 was placed mesh side up within
Teflon.RTM. ring 716. An aluminum pellet 720 was placed above
positive electrode 718, and electrolyte was added. The electrolyte
from EM Industries (Hawthorne, N.Y.) was 1 M LiPF.sub.6 in 1:1
ethylene carbonate/ dimethyl carbonate. A Teflon.RTM. o-ring is
located between top portion 704 and bottom portion 706 to
electrically insulate the two electrodes. Similarly, screws 708 are
placed within a Teflon.RTM. sleeve to electrically insulate screws
708 from top portion 704 and bottom portion 706. Electrical contact
between the battery tester and cell 700 is made by way of top
portion 704 and bottom portion 706.
[0208] The samples were tested with a discharge rate of 0.11
mA/cm.sup.2 and a charge rate of 0.08 mA/cm.sup.2, and cycled
between 1.8V to 3.4V at 25.degree. C. The measurements were
controlled by an Maccor Battery Test System, Series 4000, from
Maccor, Inc. (Tulsa, Okla.). The charging/discharging profiles were
recorded, and the discharge capacity of the active material during
each cycle was obtained.
[0209] The energy density is evaluated by the integral over the
discharge time of the voltage multiplied by the current divided by
the mass of the active material. The discharge current during
testing was 0.2 mA corresponding to a current density of 0.11
mA/cm.sup.2, and the charging current during testing was 0.16 mA
corresponding to a current density of 0.08 mA/cm.sup.2. The active
material mass ranged from about 7 to about 10 mg.
Example 4
Discharge Results With Lithium Batteries Formed With Submicron
V.sub.2O.sub.5
[0210] In this example the energy density and the specific capacity
of the crystalline V.sub.2O.sub.5 produced as described above in
Example 2 is evaluated.
[0211] Cells were produced for the four V.sub.2O.sub.5 materials
described in Example 2 (labeled samples 1-4, respectively) along
with commercial V.sub.2O.sub.5 from Cerac, Milwaukee, Wis. (labeled
sample 5). For the five cells, the open circuit voltages
immediately after sealing were about 3.4 volts. The cells were
tested at room temperature using a constant current discharge, as
described above.
[0212] The voltage as a function of capacity and energy are plotted
in FIGS. 19 and 20, respectively. Two battery samples were prepared
with the sample 4 V.sub.2O.sub.5 particles for comparison. The
specific capacity of the initial discharge for the five cells were
determined as 1) 0.4156, 2) 0.4316, 3) 0.4388, 4) 0.4454 and 5)
0.4073 ampere-hours per gram of vanadium oxide. Similarly, the
energy densities of the initial discharge for the five cells were
determined as 1) 0.1018, 2) 0.1073, 3) 0.1092, 4) 0.1114 and 5)
0.1012 Watt-hours per gram of vanadium oxide.
Example 5
Cycling Results With Lithium Batteries Formed With Submicron
V.sub.2O.sub.5
[0213] The cycling properties of cells produced with the five forms
of V.sub.2O.sub.5 were also examined. Charge and discharge
experiments were conducted at a constant current, as described
above. Each electrode contained about 7-10 mg of nanoparticles.
Thus, the currents were about 0.2 mA for discharge and about 0.15
for charge. The cells were initially discharged down to 1.8 volts
and charged to 3.4 volts.
[0214] The charging/ discharging profiles were recorded, and the
specific capacity was obtained. The specific capacity was evaluated
as the discharge capacity divided by the mass of the active
material. In FIG. 21, the discharge curves for samples 1-4 are
compared with the discharge curve for commercial V.sub.2O.sub.5
(sample 5). All of the sample lose considerable capacity over the
first cycles due to the irreversible insertion of Li into the
V.sub.2O.sub.5 matrix when discharging to 1.8 V. Batteries with the
V.sub.2O.sub.5 powders produced from the laser pyrolysis vanadium
oxides had comparable or better cycling properties to the
commercial vanadium oxides out to 50 cycles.
Examples Using Silver Vanadium Oxide Particles
[0215] The following example demonstrates the attainability of
improved battery performance using submicron silver vanadium oxide
particles for the production of lithium based batteries.
[0216] Cathode materials were produced using the silver vanadium
oxide powders described in Example 3 using the cathode production
process above. The pressed and dried disk was used as the active
cathode in a 2025 coin cell. To form the coin cell, a 1.6 square
centimeter disk of 3 mils thick nickel expanded metal (Delker,
3Ni5-077) was punched and resistance welded as a current collector
to the inside of the stainless steel cover of the 2025 coin cell
hardware (catalog No. 10769, Hohsen Corp., Osaka Japan). Battery
grade lithium foil (0.75mm thick) from Alfa Aesar, Inc. (Ward Hill,
Mass.) was punched into a two-square centimeter disk and cold
welded to the nickel expanded metal. A microporous polypropylene
separator disk (Celgard.RTM. 2400, Hoechst-Celanese, Charlotte,
N.C.) of appropriate dimensions (about 3/4 inch diameter and 1 mil
thickness) was placed over the lithium disk. The separator was
presoaked in the electrolyte of choice.
[0217] A predetermined amount of electrolyte was added to this
separator/lithium assembly. The electrolyte solution was composed
of IM LiPF.sub.6 salt. Except for Example 8, the solvent for the
electrolyte was a 1:1 by volume mixture of ethylene carbonate/DME.
In Example 8, the solvent for the electrolyte solution was selected
to evaluate the properties of the battery resulting from the
solvent. A second 1.6 square centimeter disk of 3 mil thick
stainless steel expanded metal (Delker, 3SS-(316L)7-077) was
punched and resistance welded to the inside of the stainless steel
can of the 2025 coin cell hardware. The active cathode pellet was
placed on the stainless steel expanded metal and mated with the
above separator/lithium assembly. The stainless steel can and
stainless steel cover are separated from each other by a
polypropylene grommet. The mated assembly was crimped together and
employed as a test coin cell. The cells were placed in a controlled
atmosphere chamber at 37.+-.1 degrees C. and allowed to equilibrate
for 3-4 hours prior to electrochemical testing.
[0218] The performance of the equilibrated cells under continuous
drain was evaluated as well as the performance under pulsed
operation. The measurements were controlled by a Maccor Battery
Test System, Series 4000, from Maccor, Inc. (Tulsa, Okla.). The
continuous drain measurements were made by subjecting the cells to
a constant current discharge of 0.309 mA/cm.sup.2. When the voltage
reached 1.0 volt, the discharge current was allowed to decay as the
cell voltage was held at 1.0 volt for five hours. The 1.0 volt
discharge allows for a capacity measurement independent of
polarization effects that result from discharge at finite values of
current. This yields a capacity measurement that more closely
approximates the maximum value that would be obtained with by
discharging the battery at infinitely slow discharge.
[0219] The pulse measurements were made by providing a pulse train
every thirty minutes, in which each pulse train had four-ten second
pulses spaced by 15 seconds, with each of the four pulses
corresponding to a current density of 25 mA/cm.sup.2 to a cutoff
voltage of 1.5 volts. In some of the examples, the effect of the
rate was explored more fully, as described below. For each
measurement, the discharge profile was recorded, and the discharge
capacity and energy density of the active material were
obtained.
Example 6
Lithium Batteries Formed With Submicron Silver Vanadium Oxide
Particles
[0220] In this example, the battery performance of cells with
silver vanadium oxide particles produced under different conditions
is presented. One set of cells were produced with silver vanadium
oxides produced under different reaction conditions. In addition,
the mixing speed during the synthesis of the silver vanadium oxide
on the battery performance is examined. Furthermore, the effect of
varying the silver to vanadium ratio is examined.
[0221] A set of cells were constructed with silver vanadium oxides
powders produced under different processing conditions as described
above in Example 3 from VO.sub.2 starting material. In particular,
seven samples were produced using different processing times and
temperatures for reacting the materials to produce silver vanadium
oxide: 1) 300.degree. C. for 2 hours, 2) 300.degree. C. for 4
hours, 3) 350.degree. C. for 1.5 hours, 4) 350.degree. C. for 2
hours, 5) 350.degree. C. for 4 hours, 6) 375.degree. C. for 1.5
hours and 7) 375.degree. C. for 2 hours. To form the coin cells, a
cathode pellet was formed with 140 milligrams (mg) to 150 mg of
nanoscale silver vanadium oxide. The open circuit voltage of the
seven cells immediately after crimping were 3.4 to 3.6 volts. The
cells were subjected to a constant current discharge of 0.309
milliamperes per square centimeter of active interfacial electrode
surface area. Equivalent cells were also tested under pulse
operation.
[0222] The voltage-time results for background voltage (solid
lines) and the lower pulse voltage of the first pulse of each train
(dashed lines) are illustrated in FIGS. 22 and 23. Pulse tests were
performed at a current density of 25 mA/cm.sup.2 to a cutoff
voltage of 1.5V. Background voltage is the open circuit voltage
before the first pulse of each pulse train. In high rate capable
batteries under pulse operation, the difference between the
background voltage and the pulse voltage indicates the rate
capability of the material. If the difference between the
background voltage and the pulse voltage (the delta voltage) is
small, the material shows high rate capability. Silver vanadium
oxide produced at higher temperatures and shorter time have lower
delta voltages. The best delta voltage is obtained with 350.degree.
C. processing for two hours. However, based on the pulse
performances overall processing conditions are versatile.
[0223] In addition, improved results were obtained by mixing in the
stirred oven the combination V.sub.2O.sub.5 and silver nitrate at a
higher rate of 150-200 rpm (cell 1) compared with mixing rates of
50 rpm (cell 2). The open circuit voltage of the two cells
immediately after crimping was 3.4-3.6 volts. The cells were
subjected to a constant current discharge of 0.309 milliamperes per
square centimeter of active interfacial electrode surface area.
Equivalent cells were also tested under pulse operation.
[0224] The voltage-time results for background voltage (solid
lines) and lower pulse voltage of the first pulse (dashed lines)
are illustrated in FIG. 24. Significantly improved performance was
obtained with the cathodes formed with silver vanadium oxide formed
at higher mixing speeds. Under pulse conditions, the cathodes
produced with silver vanadium oxide synthesized at a fast mixing
speed had a specific power of 861 mW/g compared with a specific
power of 863 for the battery produced with silver vanadium oxide
synthesized at a slower mixing speed. In pulse operation, the
cathode with silver vanadium oxide formed at a higher mixing speed
had about 10 percent more pulse trains when pulsed at a current
density of 25 mA/cm.sup.2 to 1.5 volts. In addition, a pulse
specific capacity of 296 mAh/g and a pulse specific energy of 664
mWh/g were obtained with silver vanadium oxide synthesized at high
mixing speeds compared with values of 283 mAh/g pulse specific
capacity and 623 mWh/g pulsed specific energy from silver vanadium
oxide synthesized at a slow mixing speed to 1.5 V.
[0225] Another set of cells were constructed as described above
with silver vanadium oxides powders with varying silver to vanadium
ratios, as described above in Example 3. The silver vanadium oxide
was produced at 350.degree. C. for four hours from a VO.sub.2
starting material. The five cells, respectively, had silver
vanadium oxide powders synthesized with vanadium to silver ratios
of 1) 1:1, 2) 1:0.95, 3) 1:0.9, 4) 1:0.875, 5) 1:0.85. The cathodes
contained 140 mg to 150 mg of nanoscale silver vanadium oxide
particles. The open circuit voltage of the five cells immediately
after crimping was 3.4 to 3.6 volts. The cells were subjected to a
constant current discharge of 0.309 milliamperes per square
centimeter of active interfacial electrode surface area. Equivalent
cells were also tested under pulse operation.
[0226] The voltage-time results for the background voltage (solid
lines) and the lower pulse voltage of the first pulse (dashed
lines) are illustrated in FIG. 25. The cathodes with higher silver
content resulted in better performance during pulse operation at a
current density of 25 mA/cm.sup.2 to 1.5 V. In particular, the
delta voltage represented by the difference in the background
voltage and the pulsed voltages was smaller for the higher silver
materials. A smaller value of delta V indicates a better high rate
material. The resulting specific capacities during pulse operation
to 1.5 volts were approximately equal to 280-290 mAh/g.
Example 7
Blended Versus Homogenized Cathode Material Compositions
[0227] In this example the improved performance of homogenized
cathode materials are presented. Furthermore, improved results are
also obtained by mixing the cathode components in a homogenizer.
The silver vanadium oxide was produced in a stirred vessel at
350.degree. C. for 4 hours from a VO.sub.2 starting material.
[0228] Cells were produced from cathode compositions that were
mixed by a homogenizer or with a blender, as described above. The
open circuit voltage of the two cells immediately after crimping
were 3.4-3.6 volts for the homogenized cathode materials and for
the blended cathode materials. The cells were subjected to a
constant current discharge of 0.309 milliamperes per square
centimeter of active interfacial electrode surface area. Equivalent
cells were also tested under pulse operation.
[0229] The voltage-time results for background voltage (solid
lines) and the lower pulse voltage of the first pulse (dashed
lines) are illustrated in FIG. 26, in which homogenized cathode
results are labeled I and blended cathode results are labeled II.
Significantly improved performance was obtained with the cathodes
formed with the homogenizer. In pulsed operation, the homogenized
cathode had about 20 percent more pulse trains when pulsed at a
current density of 25 mA/cm.sup.2 to 1.5 volts. For the homogenized
cathode, a pulsed specific capacity of 292 mAh/g and a pulsed
specific energy of 650 mWh/g were obtained compared with values for
the blended cathodes of 276 mAh/g pulsed specific capacity and 580
mWh/g pulsed specific energy to 1.5 V.
Example 8
Effects of Electrolyte Solvents
[0230] This example explores the potential of improved rate
capabilities obtainable through the use of higher ionic
conductivity solvents for the electrolyte.
[0231] Equivalent cells were produced using three different
electrolyte solvents. The first solvent was a 1:1 by volume mixture
of ethylene carbonate (EC) and DME, the second solvent was a 1:1:1
by volume mixture of ethylene carbonate, DME and triglyme (3G) and
the third solvent was a 1:1 by volume mixture of ethylene carbonate
and dimethyl carbonate (DMC). The salt was LiPF.sub.6 which was at
a one molar concentration. Equivalent cells were tested under
continuous current and under pulse operation.
[0232] The voltage-time results for background voltage (solid
lines) and lower pulse voltage of first pulse (dashed lines) are
illustrated in FIG. 27. The results under pulse operation at a
current density of 25 mA/cm.sup.2 to 1.5 V showed that the mixture
of ethylene carbonate and DME yielded better pulse performance due
to higher conductivity. In particular, the mixture of ethylene
carbonate and DME had a lower delta voltage as a function of time.
The voltage as a function of capacity is plotted in FIG. 28. The
mixture of ethylene carbonate and DME yielded significantly higher
capacity than the mixture of ethylene carbonate--DME--triglyme, and
comparable capacity to the mixture of ethylene carbonate and
dimethyl carbonate.
[0233] The pulse specific capacity and pulse specific energy are
significantly higher also for the ethylene carbonate and DME
mixture, as summarized in Table 2. The values in Table 2 for pulse
operation are at a current density of 25 mA/cm.sup.2 to 1.5 V,
while the values under continuous drain were obtained under a
current density of 0.309 mA/cm.sup.2 to 1.0 V.
2 TABLE 2 EC + EC + EC + DME + DMC DME 3G Pulsed Specific Capacity
283 285 280 (mAh/g) Pulse Specific Energy 612 646 575 (mWh/g)
Maximum Specific Power 828 884 783 (mW/g) Average Specific Power
696 763 688 (mW/g) Average Voltage (Pulse 2.157 2.279 2.054
Operation) Specific Capacity Down to 2 276 282 222 volts (mAh/g)
Specific Energy Down to 2 690 738 582 volts (mWh/g) Specific
Capacity Down to 316 315 250 1.5 volts (mAh/g) Specific Energy Down
to 1.5 792 797 630 volts (mWh/g) Specific Capacity Down to 1 362
372 310 volt (mAh/g) Specific Energy Down to 1 838 862 702 volt
(mWh/g)
Example 9
Different Electrically Conductive Particles
[0234] This example presents results obtained with silver particles
as a replacement for the graphite particles as an electrically
conductive diluent. Results were obtained at a variety of current
densities, with values at two current densities reported below.
[0235] Cells were formed with standard graphite electrically
conductive particles (A), with silver nanoparticles produced by
laser pyrolysis (B) and with commercial silver particles (C). The
silver nanoparticles were produced as described in U.S. patent
application Ser. No. 09/311,506, now U.S. Pat. No. 6,394,494 to
Reitz et al., entitled "Metal Vanadium Oxide Particles,"
incorporated herein by reference. The commercial silver particles
(1 micron average size with a surface area of 1 m.sup.2/g) were
obtained from Aldrich, Milwaukee, Wis. The voltage-time results for
background voltage (upper lines) and lower pulse voltage of first
pulse (dashed lines) with a pulse current density of 25 mA/cm.sup.2
to 1.5 V are illustrated in FIG. 29. The commercial silver
particles provided significantly worse pulse performance. The
nanoparticulate silver and the graphite produced comparable results
at 25 mA/cm.sup.2 pulse current to 1.5V.
[0236] The voltage versus time results for background voltage
(upper lines) and lower pulse voltage of the first pulse (dashed
lines) at a current density of 60 mA/cm.sup.2 to 1.5 V are
illustrated in FIG. 30. Results for both types of conductive media
are comparable at high rates.
Example 10
Effect of Cathode Thickness
[0237] This example provides an evaluation of battery performance
as a function of cathode thickness.
[0238] The cells were formed with the same cathode composition with
70 weight percent silver vanadium oxide, 10 weight percent
graphite, 10 weight percent acetylene black and 10 weight percent
Teflon.RTM.. Thus, thicker cathodes included higher weights of
silver vanadium oxide and electrically conductive particles, while
thinner cathodes included lower weights of silver vanadium oxide
and carbon. The cells were subjected to a constant current
discharge to 1 volt with a current density of 0.309 milliamperes
per square centimeter of active interfacial electrode surface area.
Equivalent cells were also tested under pulse operation.
[0239] The discharge time under continuous current is plotted in
FIG. 31. Thinner cathodes had shorter discharge times while thicker
cathodes had longer discharge times. The corresponding specific
capacities are plotted in FIG. 32. Thin electrodes with thicknesses
of 0.2 mm and 0.3 mm showed extremely high specific capacities of
424 mAh/g to 1 V Similarly, thicker cathodes had capacities of 410
mAh/g due to the longer discharge times, thereby allowing more Li
ions to intercalate through the cathode matrix. Specific energies
as a function of cathode thickness are plotted in FIG. 33. A 0.8 mm
cathode with a thickness 4 times the 0.2 mm cathode only had a loss
of 8 percent in specific energy.
[0240] The voltage-time results for background voltage (upper
lines) and lower voltage of first pulse (dashed lines) with a pulse
current density of 25 mA/cm.sup.2 to 1.5 V are illustrated in FIG.
34. Since thicker cathodes had longer discharge times, the curves
are sequential with the curves corresponding to thicker cathodes
being above the corresponding curves for thinner cathodes. The
voltage-time results for background voltage (upper lines) and lower
pulse voltage of first pulse (dashed lines) with a pulse current
density of 70 mA/cm.sup.2 are illustrated in FIG. 35. At these high
currents, thicker electrodes were able to sustain high rates. The
specific energies and specific powers down to voltages of 1.5 V as
a function of rate and thickness are plotted in FIGS. 36 and 37,
respectively. The cathode with 0.6 mm thickness had the highest
specific energy at all rates. An increase in cathode thickness
results in lower specific power at all pulse discharge rates since
thicker electrodes have higher active mass.
Example 11
Effect of Cathode Density
[0241] The performance of batteries with three different cathode
densities were evaluated. Cathodes were pressed at different
pressures to obtain the different densities.
[0242] Cathodes were produced with three densities. The 2.2 g/cubic
centimeter(cc) density was the same density used in the other
examples. In addition, cathodes were produced with densities of 1.8
g/cc and 2.6 g/cc, respectively. Generally, suitable higher density
cathodes can be produced with densities from about 2.4 g/cc to
about 2.8 g/cc. The voltage versus time results for background
voltage (upper lines) and lower pulse voltage of the first pulse
(dashed lines) with current densities of 25 mA/cm.sup.2 to 1.5 V
are illustrated in FIG. 38. Comparable results were obtained for
all densities at this pulse current density. The voltage versus
time results for background voltage (upper lines) and lower pulse
voltage of the first pulse (dashed lines) with current densities of
60 mA/cm.sup.2 to 1.5 V are illustrated in FIG. 39. These results
demonstrate that cathodes with high densities could achieve high
pulse rates.
[0243] Specific energies as a function of pulse current densities
and cathode density are summarized in FIG. 40. Moderate densities
have higher specific energies except at very high rates at which
higher density cathodes yield higher specific energies. Specific
powers as a function of pulse current densities and cathode density
are plotted in FIG. 41. Moderate densities have higher specific
powers at all rate evaluated. Cathodes with higher density yielded
similar specific powers to the moderate density cathodes at a lower
rate and higher rates.
[0244] In addition, the effect on cathode density was examined for
thicker electrodes also. The voltage versus time results for
background voltage (upper lines) and lower pulse voltage of the
first pulse (dashed lines) with current densities of 25 mA/cm.sup.2
to 1.5 V are illustrated in FIG. 42 for two densities at 0.6 mm
thickness and one density at 0.46 mm thickness. Comparable delta
voltage results were obtained for all densities and thicknesses at
this pulse current density. The voltage versus time results for
background voltage (upper lines) and lower pulse voltage of the
first pulse (dashed lines) with current densities of 70 mA/cm.sup.2
to 1.5 V are illustrated in FIG. 43 for the same densities and
thicknesses. These results demonstrate that thick cathodes with
high densities could achieve high pulse rates.
Example 12
Discharge at Different Pulse Currents
[0245] This example discloses that very high rate capabilities are
achievable with the present improved cells.
[0246] The voltage as a function of time results for background
voltage (solid lines) and lower pulse voltage of the first pulse
(dashed lines) are illustrated in FIG. 44. The pulse current
densities in FIG. 44 are 25 mA/cm.sup.2, 40 mA/cm.sup.2, 50
mA/cm.sup.2, 60 mA/cm.sup.2, 70 mA/cm.sup.2, 80 mA/cm.sup.2, and 90
mA/cm.sup.2 to 1.5 V. This demonstrates that submicron silver
vanadium oxide particles result in cathodes that are highly rate
capable up to pulse current densities of 90 mA/cm.sup.2 with a
cathode composition of 70 weight percent silver vanadium oxide, 10
weight percent graphite, 10 weight percent acetylene black and 10
weight percent Teflon.RTM..
Example 13
Evaluation of Voltage Delay
[0247] This example provides a demonstration that the batteries
described herein exhibit insignificant voltage delay in pulse
operation.
[0248] Voltage delay is a voltage drop or depression of voltage
that generally is observed for silver vanadium oxide batteries at
about 2.6 volts during pulse operation. Voltage delay is described
in detail above. Three separate tests were performed to evaluate
voltage delay. In a first test, the battery was discharged under a
constant current at a current density of 1 mA/cm.sub.2 to 2.6 V,
which is the voltage at which silver is reduced to silver metal and
expelled from the cathode matrix. When 2.6 volts was reached, a
standard accelerated pulse test was performed using the pulse
trains described above. The pulse testing was performed until the
lower pulse voltage of the first pulse reached 1.5V. The voltage as
a function of time results for background voltage (upper lines) and
lower pulse voltage of the first pulse (lower lines) are
illustrated in FIG. 45 for four pulsed current densities, 25
A/cm.sup.2, 50 mA/cm.sup.2, 60 mA/cm.sup.2 and 70 mA/cm.sup.2.
There is no evidence of a voltage delay.
[0249] The second test was identical to the first test except that
the constant current discharge was performed down to 2.5 volts. For
the second test, the voltage as a function of time results for
background voltage (upper lines) and lower pulse voltage of the
first pulse (lower lines) are illustrated in FIG. 46 for four
pulsed current densities, 25 mA/cm.sup.2, 50 mA/cm.sup.2, 60
nA/cm.sup.2 and 70 mA/cm.sup.2 to 1.5V. Again, no evidence of a
voltage delay was observed.
[0250] The third test involved an accelerated pulse test at a
current density of 60 mA/cm.sup.2 with a 100 kilo-ohm resistor
connected in series with the battery. The resistor is used to
accentuate any effect of voltage delay. When the lower pulse
voltage of the first pulse reached 1.5 volts the test was
terminated. The voltage as a function of time results for
background voltage (upper lines) and lower pulse voltage of the
first pulse (lower lines) are illustrated in FIG. 47 along with
control results without the resistor. Again, no evidence of a
voltage delay is observed.
[0251] In other silver vanadium oxide batteries, additives have
been used to try to reduce the effect of voltage delay. For
example, see U.S. Pat. No. 6,096,447, incorporated herein by
reference. With the silver vanadium oxide batteries described
herein, no additives would be needed.
[0252] The embodiments described above are intended to be
illustrative and not limiting. Additional embodiments are within
the claims below. Although the present invention has been described
with reference to preferred embodiments, workers skilled in the art
will recognize that changes may be made in form and detail without
departing from the spirit and scope of the invention.
* * * * *