U.S. patent application number 10/827072 was filed with the patent office on 2004-10-07 for lithium metal oxides.
This patent application is currently assigned to NanoGram Corporation. Invention is credited to Horne, Craig R., Kumar, Sujeet.
Application Number | 20040197659 10/827072 |
Document ID | / |
Family ID | 24385403 |
Filed Date | 2004-10-07 |
United States Patent
Application |
20040197659 |
Kind Code |
A1 |
Kumar, Sujeet ; et
al. |
October 7, 2004 |
Lithium metal oxides
Abstract
Lithium metal oxide particles have been produced having average
diameters less than about 100 nm. Composite metal oxides of
particular interest include, for example, lithium cobalt oxide,
lithium nickel oxide, lithium titanium oxides and derivatives
thereof. These nanoparticles composite metal oxides can be used as
electroactive particles in lithium or lithium ion batteries.
Batteries of particular interest include lithium titanium oxide in
the negative electrode and lithium cobalt manganese oxide in the
positive electrode.
Inventors: |
Kumar, Sujeet; (Fremont,
CA) ; Horne, Craig R.; (San Francisco, 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: |
24385403 |
Appl. No.: |
10/827072 |
Filed: |
April 19, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10827072 |
Apr 19, 2004 |
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09595958 |
Jun 19, 2000 |
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6749648 |
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Current U.S.
Class: |
429/231.3 ;
423/594.6; 423/598; 429/223; 429/224; 429/231.1 |
Current CPC
Class: |
C01G 53/52 20130101;
H01M 4/505 20130101; C01G 51/52 20130101; H01M 4/525 20130101; C01G
53/42 20130101; H01M 4/131 20130101; B82Y 30/00 20130101; H01M
4/485 20130101; C01P 2002/72 20130101; Y10T 29/49108 20150115; Y02E
60/10 20130101; C01P 2004/64 20130101; C01P 2002/54 20130101; C01G
23/005 20130101; H01M 2004/021 20130101; C01G 51/42 20130101; H01M
2004/027 20130101; C01P 2006/40 20130101; C01P 2004/04 20130101;
C01P 2004/51 20130101; H01M 10/052 20130101 |
Class at
Publication: |
429/231.3 ;
423/594.6; 429/223; 429/231.1; 423/598; 429/224 |
International
Class: |
H01M 004/52; H01M
004/50; C01G 051/04; C01G 053/04; C01G 023/04 |
Claims
What is claimed is:
1. A collection of particles comprising lithium cobalt oxide or
derivatives thereof, the collection of particles having an average
diameter less than about 100 nm.
2. The collection of particles of claim 1 wherein the lithium
cobalt oxide or derivatives thereof comprise a substituted lithium
cobalt oxide with another metal selected from the group consisting
of Ni, Mn, B, Al, Mg, Ba, Sr, Ca, Cr, Fe, V, Ti and combinations
thereof.
3. The collection of particles of claim 1 wherein the lithium
cobalt oxide or derivatives thereof comprise a substituted lithium
cobalt oxide with a stoichiometry of LiCo.sub.1-yMe.sub.yO.sub.2,
0<y.ltoreq.0.5, where Me is Ni, Mn, Al or combinations
thereof.
4. The collection of particles of claim 1 wherein the lithium
cobalt oxide or derivatives thereof comprise a substituted lithium
cobalt oxide with a stoichiometry of Li.sub.2CoMnO.sub.4.
5. The collection of particles of claim 1 wherein the lithium
cobalt oxide or derivatives thereof comprise a substituted lithium
cobalt oxide with a stoichiometry of Li.sub.2CoNiO.sub.4.
6. The collection of particles of claim 1 wherein the lithium
cobalt oxide or derivatives thereof comprise a substituted lithium
cobalt oxide with a stoichiometry of Li.sub.2CoAlO.sub.2.
7. The collection of particles of claim 1 having an average
diameter from about 5 nm to about 25 nm.
8. The collection of particles of claim 1 wherein the collection of
particles have a distribution of particle sizes such that at least
about 95 percent of the particles have a diameter greater than
about 40 percent of the average diameter and less than about 160
percent of the average diameter.
9. The collection of particles of claim 1 wherein effectively no
particles have a diameter greater than about three times the
average diameter of the collection of particles.
10. A battery comprising a cathode, the cathode comprising the
collection of particles of claim 1.
11. A collection of particles comprising lithium nickel oxide or
derivatives thereof, the collection of particles having an average
diameter less than about 100 nm.
12. The collection of particles of claim 11 wherein the lithium
nickel oxide or derivatives thereof comprise a substituted lithium
nickel metal oxide wherein the metal is selected from the group
consisting of Mn, B, Co, Al, Mg, Ba, Sr, Ca, Cr, Fe, V, Ti and
combinations thereof.
13. The collection of particles of claim 11 wherein the lithium
nickel oxide or derivatives thereof comprise lithium nickel
aluminum oxide.
14. The collection of particles of claim 11 wherein the lithium
nickel oxide or derivatives thereof comprises
Li.sub.xNi.sub.1-yMe.sub.yO.sub.2, wherein Me is Mn, B, Co, Al, Mg,
Ga, Ba, Sr, Ca, Cr, Fe, V, Ti or combinations thereof and wherein
0.8.ltoreq.x.ltoreq.1.
15. The collection of particles of claim 14 wherein
0.ltoreq.y.ltoreq.0.2.
16. The collection of particles of claim 14 wherein M is Co and
wherein 0.ltoreq.y.ltoreq.0.5.
17. The collection of particles of claim 11 wherein the particles
have an average diameter of from about 5 nm to about 25 nm.
18. The collection of particles of claim 11 wherein the collection
of particles have a distribution of particle sizes such that at
least about 95 percent of the particles have a diameter greater
than about 40 percent of the average diameter and less than about
160 percent of the average diameter.
19. The collection of particles of claim 11 wherein effectively no
particles have a diameter greater than about three times the
average diameter of the collection of particles.
20. A battery comprising a cathode, the cathode comprising the
collection of particles of claim 11.
21. A collection of particles comprising lithium titanium oxide or
derivatives thereof, wherein the collection of particles have an
average diameter less than about 100 nm.
22. The collection of particles of claim 21 wherein the lithium
titanium oxide or derivatives thereof comprises
LiTi.sub.2O.sub.4.
23. The collection of particles of claim 21 wherein the lithium
titanium oxide or derivatives thereof comprises LiTiAlO.sub.4.
24. The collection of particles of claim 21 wherein the lithium
titanium oxide or derivatives thereof comprises
LiTi.sub.2-yAl.sub.yO.sub.4, 0<y.ltoreq.1.
25. The collection of particles of claim 21 wherein the lithium
titanium oxide or derivatives thereof comprises
Li.sub.4Ti.sub.5O.sub.12.
26. The collection of particles of claim 21 wherein the lithium
titanium oxide or derivatives thereof comprises
Li.sub.1+xTi.sub.2-xO.sub.4, 0.ltoreq.x.ltoreq.1/3.
27. The collection of particles of claim 25 wherein
0.01.ltoreq.x.ltoreq.0.25.
28. The collection of particles of claim 21 wherein the lithium
titanium oxide or derivatives thereof comprises
Li.sub.4Ti.sub.3Al.sub.2O.sub.12.
29. The collection of particles of claim 21 wherein the lithium
titanium oxide or derivatives thereof comprises
Li.sub.4Ti.sub.5-yAl.sub.yO.sub.12- , 0<y.ltoreq.2.
30. The collection of particles of claim 21 wherein the particles
have an average diameter from about 5 nm to about 25 nm.
31. The collection of particles of claim 21 wherein the collection
of particles have a distribution of particle sizes such that at
least about 95 percent of the particles have a diameter greater
than about 40 percent of the average diameter and less than about
160 percent of the average diameter.
32. The collection of particles of claim 21 wherein effectively no
particles have a diameter greater than about three times the
average diameter of the collection of particles.
33. A battery comprising a anode, the anode comprising the
collection of particles of claim 21.
34. A battery comprising an anode and a cathode, the anode
comprising lithium titanium oxide and the cathode comprising
lithium manganese cobalt oxide.
35. The battery of claim 34 wherein the lithium titanium oxide
comprises LiTi.sub.2O.sub.4.
36. The battery of claim 34 wherein the lithium titanium oxide
comprises Li.sub.4Ti.sub.5O.sub.12.
37. The battery of claim 34 wherein the lithium manganese cobalt
oxide comprises Li.sub.xMnCoO.sub.4, x.ltoreq.1.
38. The battery of claim 34 wherein the lithium manganese cobalt
oxide comprises LiMnCoO.sub.4.
39. The battery of claim 34 wherein the lithium titanium oxide
comprises a collection of particles with an average diameter less
than about 100 nm.
40. The battery of claim 34 wherein the lithium titanium oxide
comprises a collection of particles with an average diameter from
about 5 nm to about 25 nm.
41. The battery of claim 34 wherein the lithium manganese cobalt
oxide comprises a collection of particles with an average diameter
less than about 100 nm.
42. The battery of claim 34 wherein the lithium manganese cobalt
oxide comprises a collection of particles with an average diameter
from about 5 nm to about 25 nm.
Description
CROSSREFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of copending U.S. patent
application Ser. No. 09/595,958 to Kumar et al., entitled Lithium
Metal Oxides," incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The invention relates to nanoparticles of lithium metal
oxides, in particular, in which the non-lithium metal includes, for
example, cobalt, nickel, titanium, or combinations thereof with one
or more additional metals. The invention further relates to
electrodes and batteries formed from the lithium metal oxide
nanoparticles.
[0003] Advances in a variety of fields have created a demand for
many types of new materials. In particular, a variety of chemical
powders can be used in many different processing contexts, such as
the production of batteries. The microminiaturization of electronic
components has created widespread growth in the use of portable
electronic devices such as cellular phones, pagers, video cameras,
facsimile machines, portable stereophonic equipment, personal
organizers and personal computers. The growing use of portable
electronic equipment has created ever increasing demand for
improved power sources for these devices. Relevant batteries
include primary batteries, i.e., batteries designed for use through
a single charging cycle, and secondary batteries, i.e., batteries
designed to be rechargeable. Some batteries designed essentially as
primary batteries may be rechargeable to some extent.
[0004] Batteries based on lithium have been the subject of
considerable development effort and are being sold commercially.
Lithium-based batteries generally use electrolytes containing
lithium ions. The negative electrodes for these batteries can
include lithium metal or alloy (lithium batteries), or compositions
that intercalate lithium (lithium ion batteries). Preferred
electroactive materials for incorporation into the positive
electrodes are compositions that intercalate lithium. The
compositions that intercalate lithium, for use in the positive
electrodes, generally are chalcogenides such as metal oxides that
can incorporate the lithium ions into their lattice.
[0005] A variety of lithium metal oxides, such as lithium cobalt
oxides, lithium nickel oxides and derivatives thereof have been
noted as promising materials for use in positive electrodes for
lithium-based batteries. Similarly, lithium titanium oxides have
been noted as promising materials for use in negative electrodes
for lithium-based batteries. These lithium metal oxides are useful
for the production of lithium-based secondary batteries. Because of
the interest in lithium metal oxides, several approaches have been
developed for producing lithium metal oxide powders.
SUMMARY OF THE INVENTION
[0006] In a first aspect, the invention pertains to a collection of
particles comprising lithium cobalt oxide or derivatives thereof,
the collection of particles having an average diameter less than
about 100 nm.
[0007] In a further aspect, the invention pertains to a collection
of particles comprising lithium nickel oxide or derivatives
thereof, the collection of particles having an average diameter
less than about 100 nm.
[0008] In another aspect, the invention pertains to a collection of
particles comprising lithium titanium oxide or derivatives thereof,
wherein the collection of particles have an average diameter less
than about 100 nm.
[0009] Moreover, the invention pertains to batteries formed from
nanoparticles of lithium cobalt oxide, lithium nickel oxide,
lithium titanium oxide or derivatives thereof.
[0010] Furthermore, the invention pertains to a battery comprising
an anode and a cathode, the anode comprising lithium titanium oxide
and the cathode comprising lithium manganese cobalt oxide.
[0011] In a further aspect, the invention pertains to a method of
producing lithium metal oxide particles wherein the lithium metal
oxide comprises a metal-1 and a metal-2, the method comprising
heating precursors particles in an oxidizing atmosphere. The
precursor particles being formed by reacting a precursor aerosol,
the aerosol comprising precursor compounds of lithium, metal-1 and
metal-2. The relative amounts of lithium, metal-1 and metal-2 are
selected to yield a desired stoichiometry of the resulting mixed
metal oxides.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] 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 collection nozzle, and the lower insert is a top
view of the injection nozzle.
[0013] 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.
[0014] 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.
[0015] FIG. 4 is a perspective view of an alternative embodiment of
a laser pyrolysis apparatus.
[0016] 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.
[0017] 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.
[0018] FIG. 7 is a perspective view of an embodiment of an
elongated reaction chamber for performing laser pyrolysis.
[0019] FIG. 8 is a schematic, sectional view of an apparatus for
heat treating nanoparticles, in which the section is taken through
the center of the apparatus.
[0020] FIG. 9 is a schematic, sectional view of an oven for heating
nanoparticles, in which the section is taken through the center of
a tube.
[0021] FIG. 10 is a schematic, perspective view of a battery of the
invention.
[0022] FIG. 11 is an x-ray diffractogram of lithium cobalt oxide
precursor nanoparticles produced by laser pyrolysis with gaseous
reactants according to the parameters specified in column 1 of
Table 1.
[0023] FIG. 12 is an x-ray diffractogram of crystalline lithium
cobalt oxide nanoparticles produced by heat treating lithium cobalt
oxide precursor nanoparticles.
[0024] FIG. 13 is a transmission electron microscopy (TEM)
micrograph of the crystalline lithium cobalt oxide
nanoparticles.
[0025] FIG. 14 is a particle size distribution produced from the
micrograph of FIG. 13.
[0026] FIG. 15 is an x-ray diffractogram of lithium nickel oxide
precursor nanoparticles produced by laser pyrolysis according to
parameters specified in Table 3.
[0027] FIG. 16 is an x-ray diffractogram of crystalline lithium
nickel oxide nanoparticles produced by heat treating lithium nickel
oxide precursor nanoparticles.
[0028] FIG. 17 is an x-ray diffractogram of lithium nickel cobalt
oxide precursor nanoparticles produced by laser pyrolysis according
to parameters specified in Table 4.
[0029] FIG. 18 is an x-ray diffractogram of crystalline lithium
nickel cobalt oxide nanoparticles produced by heat treating lithium
nickel cobalt oxide precursor nanoparticles.
[0030] FIG. 19 is an x-ray diffractogram of titanium dioxide
nanoparticles.
[0031] FIG. 20 is a transmission electron micrograph of titanium
dioxide nanoparticles.
[0032] FIG. 21 is a plot of x-ray diffractograms for lithium
titanium oxides produced from commercial titanium dioxide (upper
curve) and nanoparticles of titanium dioxide (lower curve).
[0033] FIG. 22 is a transmission electron micrograph of
nanoparticles of lithium titanium oxide with a stoichiometry of
Li.sub.4Ti.sub.5O.sub.12.
[0034] FIG. 23 is a schematic, perspective view of the three
electrode beaker cell set-up used to test the lithium intercalation
properties of crystalline lithium cobalt oxide nanoparticles.
[0035] FIG. 24 is a plot of voltage as a function of specific
capacity for the crystalline lithium cobalt nanoparticles over the
first discharge cycle.
[0036] FIG. 25 is a plot of differential capacity as a function of
voltage.
[0037] FIG. 26 is a sectional view of a two electrode test cell,
the cross section being taken through one set of screws holding the
housing together.
[0038] FIG. 27 is a plot of specific capacity as a function of
discharge cycle for crystalline lithium cobalt oxide
nanoparticles.
[0039] FIG. 28 is a plot of voltage as a function of specific
capacity for the crystalline lithium nickel cobalt nanoparticles
over the first discharge cycle.
[0040] FIG. 29 is a plot of differential capacity as a function of
voltage for nanoparticles of crystalline lithium nickel cobalt
oxide.
[0041] FIG. 30 is a plot of voltage as a function of specific
capacity for lithium titanium oxide nanoparticles and bulk lithium
titanium oxide using a beaker cell apparatus.
[0042] FIG. 31 is a plot of specific capacity as a function of
discharge cycle using a two electrode cells produced with lithium
titanium nanoparticles or bulk lithium titanium oxide
particles.
DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS
[0043] Nanoparticles of lithium cobalt oxides, lithium nickel
oxides, lithium titanium oxides and derivatives thereof are
particularly valuable materials for the production of lithium-based
batteries due to their convenient voltage ranges and reasonable
energy densities. In addition, lithium cobalt oxides are
advantageous due to their high cycle-ability. Lithium nickel oxides
are advantageous due to their high energy densities and high
specific capacities. Cobalt substituted lithium nickel oxides can
combine some of the advantages of lithium cobalt oxide and lithium
nickel oxides. Lithium titanium oxides can be used advantageously
in negative electrodes to obtain good cycling properties. The
nanoscale particles offer the possibility of producing batteries
that achieve excellent performance properties.
[0044] Lithium metal oxide nanoparticles can be formed in a two
step process using laser pyrolysis to form nanoparticle precursors
in combination with a subsequent heat treatment to transform the
precursor particles into crystalline lithium metal oxide
nanoparticles. The nanoparticle precursors can include crystalline
nanoparticles that can be identified by x-ray diffractography
and/or amorphous particles whose stoichiometry can only be
estimated based on the overall composition of the material.
[0045] In the particular embodiments described below in the
examples, a mixture of nanoparticles are produced by laser
pyrolysis that are precursors to the formation of the ultimate
lithium metal oxide. The nanoparticle mixture can be heated under
mild conditions to react the particles to produce crystalline
particles of the desired lithium metal oxide. The precursors formed
in the laser pyrolysis synthesis are selected to yield the desired
stoichiometry of the ultimate nanoparticles following heat
treatment.
[0046] A preferred approach for the formation of suitable nanoscale
lithium metal oxide precursor particles involves laser pyrolysis.
In particular, laser pyrolysis is an excellent process for
efficiently producing lithium metal oxide precursor particles with
desirable properties. A basic feature of successful application of
laser pyrolysis for the production of lithium metal oxide precursor
particles is the generation of a reactant stream containing a
lithium compound, a metal precursor compound, a radiation absorber
and a secondary reactant as an oxygen source. The reactant stream
is pyrolyzed by an intense laser beam. As the reactant stream
leaves the laser beam, the particles are rapidly quenched.
[0047] To perform laser pyrolysis, reactants can be supplied in
vapor form. Alternatively, one or more reactants can be supplied as
an aerosol. The use of an aerosol provides for the use of a wider
range of metal precursors for laser pyrolysis than are suitable for
vapor delivery only. Thus, less expensive precursors can be used
with aerosol delivery. Suitable control of the reaction conditions
with the aerosol results in nanoscale particles with a narrow
particle size distribution. The heat processing of lithium
manganese oxide nanoparticle precursors from laser pyrolysis to
form lithium manganese oxide nanocrystals is described in copending
and commonly assigned U.S. patent application Ser. No. 09/203,414,
now U.S. Pat. No. 6,136,287, Lithium Manganese Oxides and
Batteries," incorporated herein by reference.
[0048] As noted above, various forms of lithium metal oxides can
reversibly intercalate lithium atoms and/or ions. Thus, the lithium
metal oxides can function as electroactive material within a
lithium-based battery. The lithium metal oxide nanoparticles can be
incorporated into a positive electrode film or negative electrode
film, as appropriate, with a binder such as a polymer. The film
preferably includes additional electrically conductive particles
held by the binder along with the lithium metal oxide particles. A
positive electrode film can be used in a lithium battery or a
lithium ion battery. A negative electrode film can be used in a
lithium ion battery. The electrolyte for lithium and lithium ion
batteries comprises lithium ions.
[0049] Batteries based on lithium metal oxide nanoparticles can
have desirable performance characteristics. In particular, the
nanoparticles have high charging and discharging rates while
achieving good cycle-ability. In addition, the nanoparticles can be
used to produce smoother electrodes.
[0050] A. Particle Production using Laser Pyrolysis
[0051] Laser pyrolysis has been discovered to be a valuable tool
for the production of nanoscale precursor particles for further
processing into lithium metal oxide nanoparticles. The precursor
nanoparticles generally can include various crystalline and/or
amorphous nanoparticles that upon subsequent heating under mild
conditions yield crystalline lithium metal oxide nanoparticles. In
particular, the precursor nanoparticles, as described in the
examples below, with nickel and/or cobalt generally include
crystalline phases and may include nickel and/or cobalt metal
particles, lithium carbonate and nickel oxide and/or cobalt oxide.
The precursor nanopaticles for the production of oxides with
lithium and titanium include titanium oxide (TiO.sub.2).
[0052] 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 lithium metal oxide precursor 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.
[0053] Increasing the laser 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.
[0054] 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. Laser power also influences particle size with
increased laser 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.
[0055] 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.
[0056] A carrier gas can be bubbled through a liquid precursor to
facilitate delivery of a desired amount of precursor vapor.
Suitable liquid, cobalt precursors for vapor delivery include, for
example, cobalt tricarbonyl nitrosyl (Co(CO).sub.3NO), and cobalt
acetate (Co(OOCCH.sub.3).sub.3). Suitable liquid, nickel precursors
include, for example, nickel carbonyl (Ni(CO).sub.4). Suitable
liquid, titanium precursors include, for example, titanium
tetrachloride (TiCl.sub.4), titanium n-butoxide
(Ti(OC.sub.4H.sub.9).sub.4), titanium ethoxide
(Ti(OC.sub.2H.sub.5).sub.4) and titanium isopropoxide
(Ti[OCH(CH.sub.3).sub.2].sub.4). Suitable liquid, aluminum
precursors with sufficient vapor pressure of gaseous delivery
include, for example, aluminum s-butoxide
(Al(OC.sub.4H.sub.9).sub.3).
[0057] Suitable solid nickel precursors include, for example,
nickel bromide (NiBr.sub.2) and nickel iodide (NiI.sub.2). Suitable
solid titanium precursors include, for example, titanium
trichloride (TiCl.sub.3) and titanium tetrabromide (TiBr.sub.4). A
number of suitable solid, aluminum precursor compounds are
available including, for example, aluminum chloride (AlCl.sub.3),
aluminum ethoxide (Al(OC.sub.2H.sub.5).su- b.3), and aluminum
isopropoxide (Al[OCH(CH.sub.3).sub.2].sub.3). Solid precursors
generally are heated to produce a sufficient vapor pressure. A
carrier gas can be passed over the solid precursor to facilitate
delivery of the precursor vapor.
[0058] 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.
[0059] 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.
[0060] 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
several lithium metal oxide precursor nanoparticles 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.
[0061] A number of suitable solid, metal precursor compounds can be
delivered as an aerosol from solution. For example, cobaltous
iodide (CoO.sub.2), cobaltous bromide (CoBr.sub.2), cobaltous
chloride (COCl.sub.2), cobaltous acetate
(Co(CH.sub.3CO.sub.2).sub.2) and cobaltous nitrate
(Co(NO.sub.3).sub.2) are soluble in water, alcohols and other
organic solvents. In addition, nickel acetate
(Ni(CH.sub.3CO.sub.2).sub.2), nickel iodide (NiI.sub.2) and nickel
nitrate (Ni(NO.sub.3).sub.2) are soluble in water. Titanium
tetrachloride (TiCl.sub.4) is a liquid that can be directly
delivered as an aerosol. Also, suitable lithium precursors for
aerosol delivery from solution include, for example, lithium
acetate (LiCH.sub.3CO.sub.2), which is soluble in water and
alcohol, lithium chloride (LiCl), which is somewhat soluble in
water, alcohol and some other organic solvents, and lithium
hydroxide (LiOH) and lithium nitrate (LiNO.sub.3), which are
somewhat soluble in water and alcohol.
[0062] The compounds 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.
[0063] Preferred secondary reactants serving as an oxygen source
include, for example, O.sub.2, CO, CO.sub.2, O.sub.3 and mixtures
thereof. 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.
[0064] Laser pyrolysis can be performed with a variety of optical
frequencies. 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.
[0065] 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.
[0066] 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.
[0067] 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 laser 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.
[0068] 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.
[0069] 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.
[0070] The gases from precursor source 120 are mixed with gases
from infrared absorber source 124, inert gas source 126 by
combining and/or secondary reactant source 128 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.
[0071] 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. Mass
flow controllers 146 can be used to regulate the flow of gases
within the reactant delivery system of FIG. 2.
[0072] 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.
[0073] Referring to FIG. 3, another 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.
[0074] 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.
[0075] 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.
[0076] 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.
[0077] 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.
[0078] 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.
[0079] 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.
[0080] 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.
[0081] 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 10.sup.5
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.
[0082] 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.
[0083] 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.
[0084] 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.
[0085] 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.
[0086] 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.
[0087] 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.
[0088] 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.
[0089] 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.
[0090] 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.
[0091] 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. 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.
[0092] 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. 6. 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.
[0093] 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.
[0094] 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.
[0095] 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.
[0096] 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.
[0097] The design of the improved reaction chamber 460 is shown
schematically in FIG. 7. A reactant inlet 462 leads to main chamber
464. Reactant inlet 462 conforms generally to the shape of main
chamber 464. Main chamber 464 includes an outlet 466 along the
reactant/product stream for removal of particulate products, any
unreacted gases and inert gases. Shielding gas inlets 470 are
located on both sides of reactant inlet 462. 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 464 and reactant inlet 462 preferably are designed for high
efficiency particle production. Reasonable dimensions for reactant
inlet 462 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.
[0098] Tubular sections 480, 482 extend from the main chamber 464.
Tubular sections 480, 482 hold windows 484, 486 to define a light
beam path 488 through the reaction chamber 460. Tubular sections
480, 482 can include inert gas inlets 490, 492 for the introduction
of inert gas into tubular sections 480, 482.
[0099] 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. 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. The
collection apparatus can include curved components within the flow
path similar to curved portion of the collection apparatus shown in
FIG. 1.
[0100] B. Heat Treatment of Nanoparticle Precursors
[0101] Significant properties of nanoparticles 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 of atoms from other gaseous or nongaseous
compounds.
[0102] Of particular interest, it has been discovered that
nanoparticles of lithium metal oxide precursors can be formed by
laser pyrolysis. Then, a subsequent heat treatment can be used to
convert these materials into crystalline lithium metal oxide
nanoparticles. The precursors can include a mixture of materials
including, for example, crystalline metal particles, metal oxide
particles, lithium carbonate particles and one or more amorphous
materials, such as amorphous lithium metal oxides. In preferred
embodiments, the heat treatment substantially maintains the
nanoscale and size uniformity of the precursor particles.
[0103] The starting materials generally can be particles of any
size and shape, although 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.
[0104] The nanoparticles are preferably 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 at least one
starting material and the product material.
[0105] 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. However,
for the formation of lithium metal oxide nanoparticles from
corresponding precursor particles, the atmosphere preferably is
oxidizing, such that the resulting lithium metal oxide particles
have a stoichiometric amount of oxygen in the resulting crystalline
lattice.
[0106] 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.
[0107] The precise conditions can be altered to vary the type of
nanoparticles 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.
[0108] With respect to the heat treatment to form lithium metal
oxide particles, the lithium and metal stoichiometries are
determined by the laser pyrolysis process, as reflecting in the
composition of the precursor particles. The temperature and heat
treatment times can be selected to obtain complete reaction to form
crystalline lithium metal oxides, in which suitable amounts of
oxygen are obtained from the precursor particles and/or the
oxidizing atmosphere surrounding the particles during heat
treatment. In addition, for example, the temperature, time of
heating, heating and cooling rates, the gases and the exposure
conditions with respect to the gases can all be selected to yield
the desired oxidation state, crystal structure and particle size of
the resulting oxide. Generally, the lithium metal oxide precursor
nanoparticles are heat treated for sufficient periods to reach
equilibrium.
[0109] 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. 8. Apparatus 500 includes a jar 502, 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 502 is
sealed to a glass cap 504, with a Teflon.RTM. gasket 506 between
jar 502 and cap 504. Cap 504 can be held in place with one or more
clamps. Cap 504 includes a plurality of ports 508, each with a
Teflon.RTM. bushing. A multiblade stainless steel stirrer 510
preferably is inserted through a central port 508 in cap 504.
Stirrer 510 is connected to a suitable motor.
[0110] One or more tubes 512 are inserted through ports 508 for the
delivery of gases into jar 502. Tubes 512 can be made from
stainless steel or other inert material. Diffusers 514 can be
included at the tips of tubes 512 to disburse the gas within jar
502. A heater/furnace 516 generally is placed around jar 502.
Suitable resistance heaters are available from Glas-col (Terre
Haute, Ind.). One port preferably includes a T-connection 518. The
temperature within jar 502 can be measured with a thermocouple 518
inserted through T-connection 518. T-connection 518 can be further
connected to a vent 520. Vent 520 provides for the venting of gas
circulated through jar 502. Preferably vent 520 is vented to a fume
hood or alternative ventilation equipment.
[0111] Preferably, desired gases are flowed through jar 502. Tubes
512 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 502 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 (sccm) 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.
[0112] An alternative apparatus 530 for the heat treatment of
modest quantities of nanoparticles is shown in FIG. 9. The
particles are placed within a boat 532 or the like within tube 534.
Tube 534 can be produced from, for example, quartz, alumina or
zirconia. Preferably, the desired gases are flowed through tube
534. Gases can be supplied for example from inert gas source 536 or
oxidizing gas source 538.
[0113] Tube 534 is located within oven or furnace 540. Oven 540 can
be adapted from a commercial furnace, such as Mini-Mite.TM.
1100.degree. C. Tube Furnace from Lindberg/Blue M, Asheville, N.C.
Oven 540 maintains the relevant portions of the tube at a
relatively constant temperature, although the temperature can be
varied systematically through the processing step, if desired. The
temperature can be monitored with a thermocouple 542.
[0114] For the processing of lithium metal oxide precursor
nanoparticles into crystalline lithium metal oxide nanoparticles
the temperatures generally range from about 50.degree. C. to about
1000.degree. C. and in most circumstances from about 400.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.
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.
[0115] 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. 6,391,494 to Reitz et al., entitled
"Metal Vanadium Oxide Particles," and copending and commonly
assigned U.S. patent application Ser. No. 09/334,203, now U.S. Pat.
No. 6,482,374 to Kumar et al., entitled "Reaction Methods for
Producing Ternary Particles," both of which are incorporated herein
by reference.
[0116] C. Properties of the Particles
[0117] A collection of particles of interest generally has an
average diameter for the primary particles of less than about 500
nm, preferably from about 2 nm to about 100 nm, more preferably
from about 5 nm to about 75 nm, and even more preferably 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.
[0118] The primary particles usually have a roughly spherical gross
appearance. After heat treatment the particle may be less
spherical. Upon closer examination, crystalline particles generally
have facets corresponding to the underlying crystal lattice.
Nevertheless, 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. In preferred embodiments, 95 percent of
the primary particles, and preferably 99 percent, have ratios of
the dimension along the major axis to the dimension along the minor
axis less than about 2.
[0119] 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 nanometer scale of the
primary particles is clearly observable in transmission electron
micrographs of the particles. The particles generally have a
surface area corresponding to particles on a nanometer scale as
observed in the micrographs. 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.
[0120] 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.
[0121] 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 and the roughly
spherical morphology can be exploited in a variety of
applications.
[0122] In addition, the nanoparticles generally have a very high
purity level. The nanoparticles 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 nanoparticles produced by laser
pyrolysis have a high degree of crystallinity. Similarly, the
crystalline nanoparticles 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.
[0123] Lithium cobalt oxide LiCoO.sub.2 and lithium nickel oxide
LiNiO.sub.2 have cobalt and nickel both in a +3 oxidation state.
Portions of the cobalt or nickel can be replaced with other metals
to improve the cost, properties or performance of the materials in
batteries, as described further below. Lithium titanium oxide
LiTi.sub.2O.sub.4 have titanium in mixed valance states of +3 and
+4. In contrast, Li.sub.4Ti.sub.5O.sub.12 has an oxidation state of
+4. These lithium metal oxides can reversibly intercalate lithium
atoms into their lattice so that they can cycle in a secondary
lithium-based battery. In the examples below, the production of
nanoparticles of lithium cobalt oxide, lithium nickel oxide,
lithium nickel cobalt oxide, and lithium titanium oxide is
described.
[0124] In addition to the lithium metal oxide particles described
above, lithium manganese oxide nanoparticle have been produced by
laser pyrolysis with and without additional heat processing. These
particles generally have a very narrow particle size distribution,
as described above. The synthesis of lithium manganese oxide
nanoparticles is described in copending and commonly assigned U.S.
patent applications Ser. No. 09/188,768, now U.S. Pat. No.
6,607,706, entitled "Composite Metal Oxide Particles," U.S. Ser.
No. 09/203,414, now U.S. Pat. No. 6,136,287, entitled "Lithium
Manganese Oxides and Batteries," and U.S. Ser. No. 09/334,203, now
U.S. Pat. No. 6,482,374 to Kumar et al., entitled "Reaction Methods
for Producing Ternary Particles, all three of which are
incorporated herein by reference.
[0125] D. Battery Application of Lithium Metal Oxides
[0126] Referring to FIG. 10, battery 750 has an negative electrode
752, a positive electrode 754 and separator 756 between negative
electrode 752 and positive electrode 754. A single battery can
include multiple positive electrodes and/or negative electrodes.
Electrolyte can be supplied in a variety of ways as described
further below. Battery 750 preferably includes current collectors
758, 760 associated with negative electrode 752 and positive
electrode 754, respectively. Multiple current collectors can be
associated with each electrode if desired.
[0127] Lithium has been used in reduction/oxidation reactions in
batteries because it is the lightest metal and because it is the
most electropositive metal. The lithium metal oxide material has
lithium ions at lattice positions within the crystal. A variety of
lithium metal oxides are known to incorporate additional lithium
into its structure through intercalation or similar mechanisms such
as topochemical absorption.
[0128] Batteries that use lithium metal as the negative electrode
are termed lithium batteries, while batteries that use lithium
intercalation compounds as the electroactive material in the
negative electrode are termed lithium ion batteries. Some
additional terms have been used to described other lithium-based
batteries that have specific types of electrolyte/separator
structures, but herein a reference to lithium ion batteries is used
to describe all lithium-based batteries with a lithium
intercalation compound in the negative electrode regardless of the
nature of the electrolyte and separator.
[0129] Several lithium metal oxides are suitable for use as an
electroactive composition in positive electrodes of lithium-based
batteries. Lithium cobalt oxide LiCoO.sub.2 has been used
commercially in positive electrodes for the production of
lithium-based secondary batteries. Lithium cobalt oxide has a
regular layered structure that intercalates lithium and is suitable
for use in the production of 4 V batteries. Lithium cobalt oxide
has very good cycling properties in secondary batteries. However,
cobalt is relatively expensive, and lithium cobalt oxide has a
relatively low energy density.
[0130] Lithium nickel oxide is less expensive to produce and has a
higher energy density than lithium cobalt oxide. Nevertheless,
lithium nickel oxide is difficult to synthesize, which results in
poor cycling properties. In particular, during charging, lithium
nickel oxide is prone to undergo a series of phase transformations.
These transformations result in contraction of the crystal, with
resulting cracks and cleavages of the particles of electroactive
material. Due to significant rearrangement in the crystal lattice
and disorder, large losses of capacity can take place. If
sufficient lithium is lost during recharging, increasing amounts of
nickel is in the +4 oxidation state can lead to thermal instability
of the oxide and possible release of oxygen gas.
[0131] To help stabilize the cycling of lithium nickel oxide,
compounds have been generated where some of the nickel is replaced
with one or more other metals. Embodiments of the resulting
compounds can be written as Li.sub.xNi.sub.1-yMe.sub.yO.sub.2,
where x is between about 0.8 and 1.0, y generally less than 0.8 and
can be between about 0.05 and about 0.5 or between about 0.05 and
0.2, and Me is a suitable metal with an oxidation state equal to +3
or a combination of +2 and +4 in equal proportions. Preferred
metals for Me include, for example, cobalt, chromium, boron,
aluminum, barium, gallium, strontium, calcium, magnesium, iron,
titanium, manganese, vanadium and combinations thereof. One
preferred substituted lithium nickel oxide is
LiNi.sub.0.8Co.sub.0.2-yAl.sub.yO.sub.2.
[0132] For lithium nickel cobalt oxides
Li.sub.xNi.sub.1-yCO.sub.yO.sub.2, increased amounts of cobalt
relative to nickel are suitable, with y being as large as 0.5. A
thermal process for the formation of these lithium mixed metal
oxides is described in U.S. Pat. No. 5,264,201 to Dahn et al.,
entitled "Lithiated Nickel Dioxide and Secondary Cells Prepared
Therefrom," incorporated herein by reference. Batteries formed with
lithium mixed metal oxides with a metal substituted for a portion
of the nickel in lithium nickel oxide are described in U.S. Pat.
No. 5,631,105 to Hasegawa et al., entitled "Non-Aqueous Electrolyte
Lithium Secondary Batteries," incorporated herein by reference, and
in U.S. Pat. No. 5,795,558 to Aoki et al., entitled "Positive
Electrode Active Material For Lithium Secondary Battery Method Of
Producing," incorporated herein by reference.
[0133] Similarly, nickel has been substituted for a portion of the
cobalt in lithium cobalt oxide to form LiNi.sub.yCO.sub.1-yO.sub.2.
The use of the nickel substituted lithium cobalt oxide is described
in U.S. Pat. No. 4,770,960 to Nagaura et al., entitled Organic
Electrolyte Cell," incorporated herein by reference. Other metals
such as Mn, B, Al, Mg, Ba, Sr, Ca, Cr, Fe, V and Ti can also be
substituted for a portion of the cobalt in lithium cobalt oxide. In
alternative embodiments, approximately half the cobalt is replaced
with either nickel or manganese to form Li.sub.2CoNiO.sub.4 or
Li.sub.2CoMnO.sub.4, respectively.
[0134] Lithium intercalates into the lattice of the lithium metal
oxide particles in the positive electrode during discharge of the
battery. Upon discharge, the positive electrode acts as a cathode
and the negative electrode acts as an anode. The lithium leaves the
lattice of the particles in the positive electrode 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. Appropriate lithium cobalt oxides,
lithium nickel oxides and substituted forms thereof can be an
effective electroactive material for a positive electrode in either
a lithium or lithium ion battery.
[0135] Lithium ion batteries use particles in the negative
electrode of a composition that can intercalate lithium. Suitable
intercalation compounds for the negative electrode include, for
example, graphite, synthetic graphite, coke, mesocarbons, doped
carbons, fullerenes, niobium pentoxide, tin alloys, TiO.sub.2,
SnO.sub.2, and mixtures and composites thereof. Preferred
intercalation compounds for the negative electrode include certain
lithium metal oxides. For example, lithium titanium oxide is
suitable as a low voltage cathode active material or as a low
voltage anode active material. While use of lithium titanium oxide
materials in an anode reduces the overall battery voltage, this
voltage loss can be compensated for by improved cycling
properties.
[0136] Suitable lithium titanium oxide has a structure of
Li.sub.xTiO.sub.2, 0.5<x.ltoreq.1.0. Evidently, when the lithium
titanium oxide cycles in an anode, it varies from
Li.sub.0.5TiO.sub.2 (LiTi.sub.2O.sub.4) and LiTiO.sub.2. It has
been found that lithium titanium oxide based on the rutile form of
titanium oxide (TiO.sub.2) cycles better than lithium titanium
oxide based on the anatase form of titanium oxide (TiO.sub.2),
although the lithium titanium oxide material does not maintain the
crystal structure of the titanium dioxide material. The improved
cycling is based on an hexagonal form of LiTiO.sub.2, which seems
to be able to loose reversibly up to half its lithium. The cycling
of these materials is described in U.S. Pat. No. 5,464,708 to Neat
et al., entitled "Titanium Dioxide-Based Material," incorporated
herein by reference. Thermal synthesis of LiTi.sub.2O.sub.4 is
described in U.S. Pat. No. 5,911,920 to Hasezaki et al., entitled
"Manufacturing Method For Li Composite Oxides Employed As Electrode
Materials In Li Batteries," incorporated herein by reference.
[0137] Also, suitable spinel-type lithium titanium oxide particles
have been prepared with a formula Li.sub.1+xTi.sub.2-xO.sub.4,
0.ltoreq.x.ltoreq.1/3. The synthesis of these spinel-type lithium
titanium oxide particles using thermal methods is described in U.S.
Pat. No. 5,591,546 to Nagaura, entitled "Secondary Cell,"
incorporated herein by reference. In this approach,
Li.sub.2TiO.sub.3 is formed as an intermediate. As described in
this patent, improved cycle-ability was observed with
Li.sub.1+xTi.sub.2-xO.sub.4, with 0.01.ltoreq.x.ltoreq.0.25- . As
with the lithium metal oxides for the positive electrodes,
substituted forms of lithium titanium oxide can also be used. A
preferred aluminum substituted lithium titanium oxide is
Li.sub.4Ti.sub.3Al.sub.2O.- sub.12, which is an aluminum
substituted form of Li.sub.4Ti.sub.5O.sub.12.
Li.sub.4Ti.sub.3Al.sub.12 has an advantage of higher theoretical
capacity due to the lower atomic weight of aluminum compared with
titanium. Another form of aluminum substituted lithium titanium
oxide is LiTiAlO.sub.4. Generally, aluminum substituted lithium
titanium oxides can be written in the forms of
LiTi.sub.2-yAl.sub.yO.sub.4, 0<y.ltoreq.1, and
Li.sub.4Ti.sub.5-yAl.sub.yO.sub.12, 0<y.ltoreq.2.
[0138] Positive electrode 754 preferably includes electroactive
lithium metal oxide nanoparticles, such as lithium cobalt oxide
nanoparticles, lithium nickel oxide nanoparticles or substituted
forms thereof. The electroactive nanoparticles are held together
with a binder such as a polymeric binder. Nanoparticles for use in
positive electrode 754 generally can have any shape, e.g., roughly
spherical nanoparticles or elongated nanoparticles.
[0139] Negative electrode 752 can be constructed from a variety of
materials that are suitable for use with lithium ion electrolytes.
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. Suitable electroactive
lithium intercalation compounds in the form of particles,
preferably nanoparticles such as lithium titanium oxide
nanoparticles, for use in lithium ion batteries are described
above. The particles in the negative electrode generally are held
with a binder.
[0140] While some electroactive materials are reasonable electrical
conductors, an 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, stainless steel fibers and the
like.
[0141] High loadings of particles can be achieved in the binder.
Particles preferably make up greater than about 80 percent by
weight of an 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.
[0142] Current collectors 758, 760 facilitate flow of electricity
from battery 750. Current collectors 758, 760 are electrically
conductive and generally made of metal such as nickel, iron,
stainless steel, aluminum and copper and can be metal foil or
preferably a metal grid. Current collector 758, 760 can be on the
surface of their associated electrode or embedded within their
associated electrode.
[0143] The separator element 756 is electrically insulating and
provides for passage of at least some types of ions. For lithium
based batteries, the separator must provide for the passage of
lithium ions. Ionic transmission through the separator provides for
electrical neutrality in the different sections of the cell during
discharge and recharge. The separator generally prevents
electroactive compounds in the positive electrode from contacting
electroactive compounds in the negative electrode.
[0144] 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
as those suitable for use as binders. Polymer separators can be
porous to provide for ionic conduction.
[0145] Electrolytes for lithium batteries or lithium ion batteries
can include any of a variety of lithium salts. Preferred lithium
salts have inert anions and are nontoxic. 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 lithium
perfluorobutane.
[0146] 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,
1,2-dimethoxyethane, ethylene carbonate, -butyrolactone, dimethyl
sulfoxide, acetonitrile, formamide, dimethylformamide and
nitromethane.
[0147] 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 without the need for liquid solvent. In addition,
solid state separators are possible based on inorganic materials.
For example, suitable solid state electrolytes include, for
example, lithium phosphorous oxynitride (LIPON),
Li.sub.0.33La.sub.0.56TiO.sub.3 (see Brouse et al., J. Power
Sources 68:412 (1997), incorporated herein by reference) and
Li.sub.2xSr.sub.1-2xM.sub.0.5-xTi.sub.0.5+xO.sub.3 where M is a
metal, such as Cr, Fe, Co, Al, In or Y, with a preferred form being
Li.sub.0.5Sr.sub.0.5(Fe or Cr).sub.0.25Ti.sub.0.75O.sub.3 (see
Watanabe, J. Power Sources 68: 421 (1997), incorporated herein by
reference). Nanoparticles of the lithium metal oxide solid
electrolytes can be produced by the methods described herein. In
particular, Li.sub.0.33La.sub.0.56TiO.sub.3 can be formed using the
approach for lithium titanium oxide with the inclusion of an
appropriate amount of lanthanum precursor. Lanthanum chloride
(LaCl.sub.3) and lanthanum nitrate (LaNO.sub.3) are soluble in
water and alcohol and can be delivered as an aerosol precursor into
a laser pyrolysis apparatus. These lithium metal oxide solid
electrolyte nanoparticles can be deposited as a powder onto an
electrode and densified to form a thin film. Because of the small
size of the particles, very thin layers can be formed. The other
electrode can be laminated to the first electrode with the solid
electrolyte powder between the two electrodes. The thickness of the
densified solid electrolyte between the electrodes can be adjusted
to limit short circuiting and contact between positive and negative
electroactive particles to acceptable levels. The formation of thin
battery structures based on nanoparticles is described further in
copending and commonly assigned U.S. patent application Ser. No.
09/435,748 to Buckley et al., entitled "Electrodes," incorporated
herein by reference. Also, the formation of separators from
densified nanoparticles is described in U.S. Pat. No. 5,905,000 to
Yadev et al., entitled "Nanostructured Ion Conducting Solid
Electrolytes," incorporated herein by reference.
[0148] The shape of the battery components can be adjusted to be
suitable for the desired final product, for example, a coin
battery, a rectangular construction or a cylindrical battery. The
battery generally includes a casing with appropriate components 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
electrical and ionic resistances 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.
PARTICLE SYNTHESIS EXAMPLES
EXAMPLE 1
Lithium Cobalt Oxide
[0149] This example describes the production of lithium cobalt
oxide nanoparticles. Initially, the synthesis of lithium cobalt
oxide precursor particles was performed by laser pyrolysis. Laser
pyrolysis was carried out using a reaction chamber essentially as
described above with respect to FIGS. 4-6.
[0150] Cobalt nitrate (Co(NO.sub.3).sub.2.6H.sub.2O) (Alfa Aesar,
Inc., Ward Hill, Mass.) precursor and lithium nitrate (LiNO.sub.3)
(Alfa Aesar, Inc.) precursor were dissolved in deionized water. Two
different concentrations of solutions were used, as specified in
Table 1. The aqueous metal precursor solutions were carried into
the reaction chamber as an aerosol. C.sub.2H.sub.4 gas was used as
a laser absorbing gas, and Argon was used as an inert gas. The
reactant mixture containing cobalt nitrate, lithium nitrate, Ar,
O.sub.2 and C.sub.2H.sub.4 was introduced into the reactant nozzle
for injection into the reaction chamber. Additional parameters of
the laser pyrolysis synthesis relating to the particles of Example
1 are specified in Table 1.
1TABLE 1 1 2 Crystalline Phases cobalt, cobalt oxide cobalt, cobalt
oxide (CoO), Li.sub.2CO.sub.3 (CoO), Li.sub.2CO.sub.3 Pressure
(Torr) 150 150 Argon F.R.-Window 5 5 (SLM) Argon F.R.-Shielding 20
20 (SLM) Ethylene (SLM) 4.75 4.75 Carrier Gas (Argon) 11 11 (SLM)
Oxygen (SLM) 5.1 5.1 Laser Input (Watts) 1200 1200 Laser Output
(Watts) 850 920 Production Rate (g/hr) 8.4 2.1 Precursor 1.49 M
cobalt nitrate, 0.75 M cobalt nitrate, 1.93 M lithium nitrate 0.97
M lithium nitrate slm = standard liters per minute Argon - Win. =
argon flow through inlets 216, 218 Argon - Sld. = argon flow
through annular channel 142.
[0151] To evaluate the atomic arrangement, the samples were
examined by x-ray diffraction using the Cr(K.alpha.) radiation line
on a Rigaku Miniflex x-ray diffractometer. X-ray diffractograms for
a sample produced under the conditions specified in the first
column of Table 1 is shown in FIG. 11. Crystalline phases were
identified that corresponded to cobalt metal, cobalt oxide (CoO)
and lithium carbonate (Li.sub.2CO.sub.3). The precursor particles
produced under the conditions in the second column of Table 1 had
an x-ray diffractogram similar to the diffractogram shown in FIG.
11.
[0152] A sample of lithium cobalt oxide precursor nanoparticles
produced by laser pyrolysis according to the conditions specified
in the first column of Table 1 was heated in an oven under
oxidizing conditions. The oven was essentially as described above
with respect to FIG. 9. Between about 100 and about 700 mg of
nanoparticles were placed in an open 1 cc boat within the quartz
tube projecting through the oven. Air was flowed through a 3.0 inch
diameter quartz tube at a flow rate of 450 sccm. The oven was
heated to about 675.degree. C. The particles were heated for about
5 hours. Similarly, a sample produced under the conditions in the
second column of Table 1 were heated at 590.degree. C. for five
hours in air. When the samples were heated at temperatures greater
than about 700.degree. C., significant particle growth was
observed. When the particles were heated at temperatures less than
about 500.degree. C. a low temperature phase of lithium cobalt
oxide was formed that exhibited a lower specific energy over a four
volt lithium battery discharge range.
[0153] The crystal structure of the resulting heat treated
particles was determined by x-ray diffraction. The x-ray
diffractogram for heated sample from the first column of Table 1 is
shown in FIG. 12. The x-ray diffractogram shown in FIG. 12
indicates that the collection of particles included crystals of
LiCoO.sub.2. LiCoO.sub.2 is reported to have a rhombohedral crystal
structure.
[0154] Transmission electron microscopy (TEM) was used to evaluate
particle sizes and morphology of the heat treated samples. A TEM
photograph of the lithium cobalt oxide particles produced following
heat treatment of precursor particles formed under the conditions
in the first column of Table 1 are shown in FIG. 13. An examination
of a portion of the TEM micrograph yielded an average particle size
of about 40 nm. The corresponding particle size distribution is
shown in FIG. 14. The approximate size distribution was determined
by manually measuring diameters of the particles distinctly visible
in the micrograph of FIG. 13. Only those particles having clear
particle boundaries were measured to avoid regions distorted or out
of focus in the micrograph. Measurements so obtained should be more
accurate and are not biased since a single view cannot show a clear
view of all particles. It is significant that the particles span a
rather narrow range of sizes. Some necking and agglomeration is
observed in the TEM micrographs. The average dimension of
nonspherical particles was used in plotting the particle size
distribution.
[0155] Also, BET surface areas were measured for the two precursor
particle samples produced by laser pyrolysis under the conditions
specified in columns 1 and 2 of Table 1 and for portions of the
samples following heat treatment. The BET surface area was
determined with an N.sub.2 gas absorbate. The BET surface area was
measured with a Micromeritics Tristar 3000.TM. instrument. The
results are shown in Table 2.
2 TABLE 2 1 1H.sup.1 2 2H.sup.2 Surface Area 44 7 101 17
(m.sup.2/gm) .sup.1Sample 1H is sample 1 of Table 1 following heat
treatment as described above. .sup.2Sample 2H is the sample 2 of
Table 1 following heat treatment as described above.
[0156] The drop in BET surface area following heat treatment is
consistent with grain growth and agglomeration due to the heating
process.
EXAMPLE 2
Lithium Nickel Oxide
[0157] This example describes the production of lithium nickel
oxide nanoparticles. Initially, the synthesis of lithium nickel
oxide precursor particles was performed by laser pyrolysis. Laser
pyrolysis was performed using an apparatus essentially as described
above with respect to FIGS. 4-6.
[0158] Nickel nitrate (Ni(NO.sub.3).sub.2.6H.sub.2O) (Alfa Aesar,
Inc., Ward Hill, Mass.) precursor and lithium nitrate (LiNO.sub.3)
(Alfa Aesar, Inc.) precursor were dissolved in deionized water with
concentration as noted in Table 3. The aqueous metal precursor
solutions were carried into the reaction chamber as an aerosol.
C.sub.2H.sub.4 gas was used as a laser absorbing gas, and Argon was
used as an inert gas. The reactant mixture containing nickel
nitrate, lithium nitrate, Ar, O.sub.2 and C.sub.2H.sub.4 was
introduced into the reactant nozzle for injection into the reaction
chamber. Additional parameters of the laser pyrolysis synthesis
relating to lithium nickel oxide precursor particles are specified
in Table 3.
3 TABLE 3 1 Crystalline Phases nickel, nickel oxide (NiO),
Li.sub.2CO.sub.3, amorphous phases Pressure (Torr) 150 Argon
F.R.-Window 5 (SLM) Argon F.R.-Shielding 20 (SLM) Ethylene (SLM)
4.75 Carrier Gas (Argon) 12 (SLM) Oxygen (SLM) 5.1 Laser Input
(Watts) 1207 Laser Output (Watts) 1010 Production Rate (g/hr) 4.9
Precursor 1.54 M nickel nitrate, 2.0 M lithium nitrate slm =
standard liters per minute Argon - Win. = argon flow through inlets
216, 218 Argon - Sld. = argon flow through annular channel 142.
[0159] To evaluate the atomic arrangement, the samples were
examined by x-ray diffraction using the Cr(K.alpha.) radiation line
on a Rigaku Miniflex.TM. x-ray diffractometer. X-ray diffractograms
for a sample produced under the conditions specified in Table 3 is
shown in FIG. 15. Crystalline phases were identified that
corresponded to nickel metal, nickel oxide (NiO) and lithium
carbonate (Li.sub.2CO.sub.3).
[0160] A sample of lithium nickel oxide precursor nanoparticles
produced by laser pyrolysis according to the conditions specified
in Table 3 was heated in an oven under oxidizing conditions. The
oven was essentially as described above with respect to FIG. 9.
Between about 100 and about 300 mg of nanoparticles were placed in
an open 1 cc boat within the quartz tube projecting through the
oven. Air was flowed through a 1.0 inch diameter quartz tube at a
flow rate of 200 cc/min. The oven was heated in air to about
400.degree. C. for about 1 hour and then to about 750.degree. C.
for about 3 hours.
[0161] The crystal structure of the resulting heat treated
particles were determined by x-ray diffraction. The x-ray
diffractograrn for the heated sample with precursors produced under
the conditions listed in Table 3 is shown in FIG. 16. The x-ray
diffractogram shown in FIG. 16 indicates that the collection of
particles involved crystals of LiNiO.sub.2.
EXAMPLE 3
Lithium Nickel Cobalt Oxide
[0162] This example describes the production of lithium nickel
cobalt oxide nanoparticles. Initially, the synthesis of lithium
nickel cobalt oxide precursor particles was performed by laser
pyrolysis. The laser pyrolysis was performed in a reaction chamber
essentially as described above with respect to FIGS. 4-6.
[0163] Nickel nitrate (Ni(NO.sub.3).sub.2.6H.sub.2O) (Alfa Aesar)
precursor, cobalt nitrate (Co(NO.sub.3).sub.2.6H.sub.2O) (Alfa
Aesar) precursor and lithium nitrate (LiNO.sub.3) (Alfa Aesar)
precursor were dissolved in deionized water at concentrations as
noted in Table 4. The aqueous metal precursor solutions were
carried into the reaction chamber as an aerosol. C.sub.2H.sub.4 gas
was used as a laser absorbing gas, and Argon was used as an inert
gas. The reactant mixture containing nickel nitrate, cobalt
nitrate, lithium nitrate, Ar, O.sub.2 and C.sub.2H.sub.4 was
introduced into the reactant nozzle for injection into the reaction
chamber. Additional parameters of the laser pyrolysis synthesis for
producing lithium nickel cobalt oxide precursor particles are
specified in Table 4.
4 TABLE 4 1 Crystalline Phases nickel, nickel oxide (NiO),
LiCO.sub.3, amorphous phases Pressure (Torr) 150 Argon F.R.-Window
5 (SLM) Argon F.R.-Shielding 20 (SLM) Ethylene (SLM) 4.75 Carrier
Gas (Argon) 12 (SLM) Oxygen (SLM) 5.1 Laser Input (Watts) 1207
Laser Output (Watts) 1030 Production Rate (g/hr) 3.64 Precursor
1.74 M nickel nitrate, 0.35 M cobalt nitrate, 2.25 M lithium
nitrate slm = standard liters per minute Argon - Win. = argon flow
through inlets 216, 218 Argon - Sld. = argon flow through annular
channel 142.
[0164] To evaluate the atomic arrangement, the samples were
examined by x-ray diffraction using the Cr(K.alpha.) radiation line
on a Rigaku Miniflex.TM. x-ray diffractometer. X-ray diffractograms
for a sample produced under the conditions specified in Table 4 is
shown in FIG. 17. Crystalline phases were identified that
corresponded to nickel metal, nickel oxide (NiO) and lithium
carbonate (Li.sub.2CO.sub.3). Some amorphous phase material may
also be present.
[0165] A sample of lithium nickel cobalt oxide precursor
nanoparticles produced by laser pyrolysis according to the
conditions specified in Table 4 was heated in an oven under
oxidizing conditions. The oven was essentially as described above
with respect to FIG. 9. Between about 100 and about 700 mg of
nanoparticles were placed in a boat within the quartz tube
projecting through the oven. Air was flowed through a 1.0 inch
diameter quartz tube at a flow rate of 200 cc/min. The oven was
heated in air to about 400.degree. C. for about 1 hour and then to
about 675.degree. C. for about 3 hours.
[0166] The crystal structure of the resulting heat treated
particles were determined by x-ray diffraction. The x-ray
diffractogram for heated sample with precursors produced under the
conditions listed in Table 4 is shown in FIG. 18. The x-ray
diffractogram shown in FIG. 18 indicates that the collection of
particles included crystals of lithium nickel cobalt oxide. The
precursors were introduced at a concentration to target a
composition of LiNi.sub.0.8Co.sub.0.20O.sub.2.
EXAMPLE 4
Lithium Titanium Oxide Nanoparticles
[0167] The production of nanoparticles of lithium titanium oxide
(Li.sub.4Ti.sub.5O.sub.12) is described in this example. The
lithium titanium oxide nanoparticles were produced in a two step
process. In the first step, titanium oxide nanoparticles were
produced by laser pyrolysis. In the second step, a mixture of
titanium oxide nanoparticles and lithium hydroxide were heated.
[0168] The titanium oxide particles were produced using essentially
a laser pyrolysis apparatus shown in FIG. 1 of U.S. Pat. No.
5,938,979 to Kambe et al., entitled "Electromagnetic Shielding,"
incorporated herein by reference. Titanium tetrachloride (Strem
Chemical, Inc., Newburyport, Mass.) precursor vapor was carried
into the reaction chamber by bubbling Ar gas through TiCl.sub.4
liquid in a container at room temperature. C.sub.2H.sub.4 gas was
used as a laser absorbing gas, and argon was used as an inert gas.
The reaction gas mixture containing TiCl.sub.4, Ar, O.sub.2 and
C.sub.2H.sub.4 was introduced into the reactant gas nozzle for
injection into the reaction chamber. The reactant gas nozzle had an
opening with dimensions of 5/8 in.times.1/8 in. The production rate
of titanium dioxide particles was typically about 4 g/hr.
Additional parameters of the laser pyrolysis synthesis relating to
the titanium oxide particles are specified in Table 5.
5 TABLE 5 1 Crystalline Phases Anatase & Rutile Pressure (Torr)
320 Argon F.R.-Window 700 (SCCM) Argon F.R.-Shielding 7.92 (SLM)
Ethylene (SLM) 1.34 Carrier Gas (Argon) 714 (SCCM) Oxygen (SCCM)
550 Laser Output (Watts) 450 Nozzle Size 5/8 in .times. 1/8 in sccm
= standard cubic centimeters per minute slm = standard liters per
minute Argon - Win. = argon flow through inlets 216, 218 Argon -
Sld. = argon flow through annular channel 142.
[0169] To evaluate the atomic arrangement, the samples were
examined by x-ray diffraction using the Cr(K.alpha.) radiation line
on a Rigaku Miniflex.TM. x-ray diffractometer. X-ray diffractograms
for a sample produced under the conditions specified in Table 5 is
shown in FIG. 19. The titanium dioxide particles had a crystal
structure indicating mixed phases of anatase titanium dioxide and a
small portion of rutile titanium dioxide. The diffractogram has a
broad peak at about 23.degree. and at low scattering angles
indicative of amorphous carbon. The amorphous carbon coating can be
removed upon subsequent heating.
[0170] Transmission electron microscopy (TEM) was used to determine
particle sizes and morphology. A TEM micrograph for the particles
produced under the conditions of Table 5 is displayed in FIG. 20.
The particles had facets corresponding to the crystal lattice of
the titanium oxide.
[0171] An elemental analysis of the particles was performed. The
particles included 55.18 percent by weight carbon and 19.13 percent
by weight titanium. Chlorine contamination was found to be 0.42
percent by weight. Oxygen was not directly measured but presumably
accounted for most of the remaining weight. The elemental analysis
was performed by Desert Analytics, Tucson, Ariz.
[0172] To produce the lithium titanium oxide particles, 3.67 g
LiOH.H.sub.2O (Alfa Aesar, Inc., Ward Hill, Mass.) and 8.70 g
TiO.sub.2 nanoparticles (as described above) were mixed together
using 22.9 g diglyme as a dispersant. Other dispersants can be used
as long as they do not dissolve either reactant. The mixture was
combined with 3 mm yttria-stabilized zirconia grinding media in a
polypropylene bottle (Union Process, Akron, Ohio). The slurry with
the grinding media was mixed for two hours in a shaker mill (SPEX
Certiprep, Inc., Metuchen, N.J.).
[0173] After mixing the slurry was poured through a sieve to remove
the grinding media. The grinding media was rinsed with additional
diglyme to remove additional material from the grinding media.
Following removal of the grinding media, the slurry was vacuum
filtered to remove the solvent and to collect the power on filter
paper. The powder was transferred from the filter paper to a glass
petri dish.
[0174] To remove the remaining solvent, the material was heated at
160.degree. C. for 10 hours under vacuum. The solvent was collected
in a trap. To perform the conversion of the material to lithium
titanium oxide, the dried material was heated in an alumina boat
within a one inch tube furnace, as shown schematically in FIG. 9.
O.sub.2 is flowed through the tube at a rate of 40 cc/min. The heat
treatment was continued for 20 hours at 800.degree. C. For
comparison commercial TiO.sub.2 was processed into
Li.sub.4Ti.sub.4O.sub.12 in the same way.
[0175] The crystal structures of the resulting heat treated
particles were determined by x-ray diffraction using the
Cr(K.alpha.) radiation line on a Rigaku Miniflex.TM. x-ray
diffractometer. The x-ray diffractograms for the heated samples are
shown in FIG. 21. The upper curve is the diffractogram obtained
from the lithium titanium oxide formed from commercial TiO.sub.2,
and the lower curve is the diffractogram obtained from the lithium
titanium oxide formed from nanoparticulate TiO.sub.2. The line plot
at the bottom of FIG. 21 indicates the known positions and relative
intensities of an x-ray diffractogram for Li.sub.4Ti.sub.5O.sub.12.
From a review of the x-ray diffractograms, the synthesized lithium
titanium oxide particles had a stoichiometry corresponding to
Li.sub.4Ti.sub.5O.sub.12.
[0176] A transmission electron micrograph (TEM), shown in FIG. 22,
was obtained for the lithium titanium oxide nanoparticles. From the
TEM photo, the particles had an average particle diameter of about
200 nm. TEM analysis of the TiO.sub.2 nanoparticles indicated a
bimodal distribution of particle sizes with average particles sizes
of about 15 nm and about 100 nm. A bimodal distribution is
generally indicative of a blend of two types of particles with
different compositions. It was not know if the distribution of
smaller nanoparticles corresponded to carbon particles or titanium
oxide particles.
BATTERY TESTING EXAMPLES
EXAMPLE 5
Discharge Properties of Crystalline Lithium Cobalt Oxide
Nanoparticles
[0177] The properties of crystalline lithium cobalt oxide
nanoparticles produced by heat treatment of nanoparticle precursors
synthesized by laser pyrolysis was examined using a beaker cell
test. The lithium cobalt oxide nanoparticles were produced by a
heat treatment as described in Example 1 using the precursors
synthesized under the conditions specified in the first column of
Table 1.
[0178] To produce the batteries for beaker cell testing, the
lithium cobalt oxide (LCO) powders were mixed with a conductive
acetylene black powder (Catalog number 55, Chevron Corp.) at a
ratio of 60:30. The powder mixture was ground with a mortar and
palette to thoroughly mix the powders.
[0179] A few drops of polyvinylidene fluoride (PVDF) solution were
added to the homogeneous powder mixture. The 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 final ratio of LCO:AB:PVDF was
60:30:10. The resulting slurry was spread onto a preweighed
aluminum metal mesh. The mesh with the slurry was baked in a vacuum
oven overnight at 120.degree. C. to remove the solvent and residual
moisture. After removal from the oven, the electrodes were
immediately placed in a glove box (Vacuum Atmosphere Co.,
Hawthorne, Calif.) under an argon atmosphere and weighted
again.
[0180] All discharge/charge experiments were conducted in the glove
box. The water and oxygen concentrations in the glove box were
measured to be less than 1 ppm and 1.5 ppm, respectively. In a
first set of experiments, the samples were tested in a three
electrode configuration, as shown in FIG. 23. In the battery test
set up 800, cathode 802 on aluminum mesh 804 is place in container
806. Container 806 holds liquid electrolyte 808. Counter electrode
810 and reference electrode 812 are also placed into container 806.
Lithium metal was used as both counter electrode and reference
electrode. The electrodes are connected to a battery testing system
814.
[0181] No separator is needed for this testing configuration since
the electrodes are physically separated. Alternatively, the liquid
electrolyte can be viewed as the separator. The liquid electrolyte
(from Merck & Co., Inc.) was 1M LiClO.sub.4 in propylene
carbonate.
[0182] Charge and discharge experiments were conducted at an
approximately constant current equivalent to about 5 mA per gram of
oxide within the electrode. Each electrode contained about 10 mg of
nanoparticles. Thus, the currents were about 0.05 mA. If the
material were pure lithium cobalt oxide, this charge/discharge rate
corresponds to a rate of C/30 (i.e., a rate such that the cathode
would be fully discharged in 30 hours). The cells were initially
charged from their open-circuit voltage up to 4.3 volts and then
discharged down to 2.0 volts.
[0183] The measurements were controlled by an Arbin Battery Testing
System, Model BT4023, from Arbin Instruments, College Station, Tex.
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.
Also, the differential capacity (.delta.x/.delta.V) was determined
by taking the derivative of the discharge capacity with respect to
voltage. Therefore, the differential capacity is the inverse slope
of the charge and discharge profile with respect to voltage. Peaks
in the plot of differential capacity versus voltage indicate
voltages where lithium inserts into the host material. In a lithium
metal cell, the cell voltage is approximately proportional to the
chemical potential of Li.sup.+ in the host material. Therefore, the
differential capacity can be used to characterize and/or identify
the material and its structure.
[0184] A discharge curve is plotted in FIG. 24 for two comparably
prepared samples. The lithium cobalt oxide nanoparticles displayed
a discharge capacity of about 145 mAh/gm. The differential capacity
of the nanoparticles is plotted in FIG. 25 over a charging cycle
and a discharging cycle. The shape of the curves are characteristic
of the material, i.e., lithium cobalt oxide, and provide
information about the lithium intercalation into the lattice.
EXAMPLE 6
Cycling Properties of Lithium Cobalt Oxide Nanoparticles
[0185] In this example the battery cycling properties of the
crystalline nanoparticles of lithium cobalt oxide were evaluated.
The lithium cobalt oxide nanoparticles were produced by a heat
treatment as described in Example 1 using the precursors
synthesized under the conditions specified in the first column of
Table 1.
[0186] To prepare the samples, the lithium cobalt oxide powders
(LCO) were combined with graphite powder (KS-4, Timcal, Westlake,
Ohio) with an average particle size of about 4 microns and carbon
black powder (BP2000, Timcal, Westlake, Ohio) with an average
particle size of about 12 nm, as conductive diluents. The dry
powders were blended with a mortar and pestle with a 12% by weight
dispersion of poly(vinydene fluoride) (PVdF) (Type 301F, Elf
Atochem) in n-methyl-pyrrolidinone solvent. The PVDF serves as a
binder. The solids in the resultant formulation was 78% by weight
lithium cobalt oxide, 10% by weight carbon (about equal amounts of
graphite and carbon black) and 12% by weight PVdF. The dispersion
was mixed well and coated at a thickness of 200 microns onto an
aluminum foil.
[0187] An approximately two-square centimeter disk was cut from the
coated foil sheet, dried and pressed at 40,000 to 50,000 pounds
over the two square centimeters to densify the coating. The
compressed disk was vacuum dried and weighed. After drying, the
disk had a thickness of about 19 microns and a density of
approximately 3.1 g/cc.
[0188] The samples were tested in an cell 830 with an airtight
two-electrode configuration shown in FIG. 26. The casing 832 for
the sample battery was obtained from Hohsen Co., Osaka, Japan. The
casing included a top portion 834 and a bottom portion 836, which
are secured with four screws 838. The two other screws not shown in
FIG. 26 are behind the two screws shown. Lithium metal (Alfa/Aesar,
Ward Hill, Mass.) was used as a negative electrode 842. Negative
electrode 842 was placed within the bottom portion 836. A separator
844, Celgard.RTM. 2400 (Hoechst Celanese, Charlotte, N.C.), was
placed above the lithium metal. A Teflon.RTM. ring 846 was placed
above separator 844. A positive electrode 848 was placed mesh side
up within Teflon.RTM. ring 846. An aluminum pellet 850 was placed
above positive electrode 848, and electrolyte was added. The
electrolyte from EM Industries (Hawthorne, N.Y.) was 1M LiPF.sub.6
in 1:1 ethylene carbonate/dimethyl carbonate. A Teflon.RTM. o-ring
is located between top portion 834 and bottom portion 836 to
electrically insulate the two electrodes. Similarly, screws 838 are
placed within a Teflon.RTM. sleeve to electrically insulate screws
838 from top portion 834 and bottom portion 836. Electrical contact
between the battery tester and cell 830 is made by way of top
portion 834 and bottom portion 836.
[0189] The samples were tested with a discharge/charge rate at a
constant current of 0.5 mA/cm.sup.2, and cycled between 3.3V to
4.25V at 25.degree. C. The measurements were controlled by an Arbin
Battery Testing System, Model BT4023, from Arbin Instruments,
College Station, Tex. The charging/discharging profiles were
recorded, and the discharge capacity of the active material was
obtained.
[0190] 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 current during testing was 1
mA, corresponding to a current density of 0.5 mA/cm.sup.2. The
active material mass ranged from about 30 to about 50 mg.
[0191] The specific capacity as a function of discharge cycle is
plotted in FIG. 27. The specific capacity and cycling properties
are comparable to values obtained with commercially available
lithium cobalt oxide. Only 12% fading was observed after 65 cycles
even against lithium anodes, which are not the optimal material for
obtaining good cycling properties.
EXAMPLE 7
Beaker Cell Testing of Lithium Nickel Cobalt Oxide
[0192] The properties of crystalline lithium nickel cobalt oxide
(LiNi.sub.0.8Co.sub.0.2O.sub.2) nanoparticles produced by heat
treatment of nanoparticle precursors synthesized by laser pyrolysis
was examined using a beaker cell test. The lithium nickel cobalt
oxide nanoparticles were produced by a heat treatment as described
in Example 3 using the precursors synthesized under the conditions
specified in Table 4.
[0193] The lithium nickel cobalt oxide electrodes for beaker cell
testing were produced, as described above in Example 5. All
discharge/charge experiments were conducted in a glove box, as
described in Example 5. The samples were tested in a three
electrode configuration, as shown in FIG. 23. In the battery test
set up 800, cathode 802 on aluminum mesh 804 is place in container
806. Container 806 holds liquid electrolyte 808. Counter electrode
810 and reference electrode 812 are also placed into container 806.
Lithium metal was used as both counter electrode and reference
electrode. The electrodes are connected to a battery testing system
814. No separator was needed for this testing configuration. The
liquid electrolyte (from Merck & Co., Inc.) was 1M LiClO.sub.4
in propylene carbonate.
[0194] Charge and discharge experiments were conducted at an
approximately constant current equivalent to about 5 mA per gram of
oxide within the electrode. Each electrode contained about 10 mg of
nanoparticles. Thus, the currents were about 0.05 mA. The cells
were initially charged from their open-circuit voltage up to 4.3
volts and then discharged down to 2.0 volts.
[0195] A discharge curve is plotted in FIG. 28 for two comparably
prepared samples. The lithium nickel cobalt oxide nanoparticles
displayed a discharge capacity of about 199.5 mAh/gm for the first
electrode and 182.3 mAh/gm for the second electrode. The
differential capacity of the nanoparticles is plotted in FIG. 29
over a charging cycle and a discharging cycle.
EXAMPLE 8
Beaker Cell Testing of Lithium Titanium Oxides
[0196] The specific capacity of nanoparticles of lithium titanium
oxide (Li.sub.4Ti.sub.5O.sub.12) particles was evaluated in a
beaker cell test.
[0197] The experiment was set up in a beaker cell as described
above in Example 5. A discharge rate of 5 mA/g was used. The
cathode incorporating lithium titanium oxide nanoparticles was
prepared as described in Example 5. Lithium metal was used as the
anode.
[0198] A plot of voltage as a function of specific capacity is
shown in FIG. 30. The solid line plot indicates the results for
nanoparticles of lithium titanium oxide, and the dashed line plot
indicates the results obtained with the lithium titanium oxide
produced from commercial titanium dioxide (bulk lithium titanium
oxide). The lithium titanium oxide nanoparticles had a specific
capacity of about 180 mAh/g to a 1.0 V cutoff with almost 90% of
the capacity at about 1.55 volts. The results were reproducible in
additional cells. For these material, the bulk lithium titanium
oxide had a discharge capacity of about 7 % higher than the
corresponding nanoparticles, and the nanoparticulate lithium
titanium oxide had a discharge voltage about 35 mV lower than the
corresponding bulk material.
EXAMPLE 9
Cycling Properties of Lithium Titanium Oxide Nanoparticles
[0199] In this example, the cycling properties of lithium titanium
oxide (Li.sub.4Ti.sub.5O.sub.12) are presented.
[0200] Two electrode cells were produced as described in Example 6
with the following changes. The cathodes were produced using
lithium titanium oxide powders produced as described in Example 4
with 78 percent by weight lithium titanium oxide, 10 percent by
weight carbon and 12 percent by weight PVdF binder (type 741
nanoparticles and type 301F for commercial/bulk lithium titanium
oxide). For the Li.sub.4Ti.sub.5O.sub.12 nanoparticle containing
electrodes, the carbon was a one-to-one ratio of compressed carbon
black (H-M Royal, Buena Park, Calif.) and KS-4 graphite (4 micron
round graphite, Timcal Corp., Westlake, Ohio). In the electrode
produced with the bulk Li.sub.4Ti.sub.5O.sub.12, the carbon was a
mixture of BP 2000 with an average 12 nm diameter size (Cabot
Corp., Billerica, Mass.) and KS-4 graphite.
[0201] A comparison of the electrochemical cycling stability
between nanoparticles of Li.sub.4Ti.sub.5O.sub.12 and particles
produced from commercial titanium dioxide is shown in FIG. 31. The
cells were cycled between 2.0 volts and 1.3 volts. The data for the
nanoparticles of Li.sub.4Ti.sub.5O.sub.12 is an average over two
cell while the cycling results from the bulk lithium titanium oxide
powders were obtained with only one cell. The discharge rate beyond
the first cycle for the cell formed with nanoparticles of lithium
titanium oxide was about three times greater than form the cell
made with bulk lithium titanium oxide (about 30 mA/g versus about
11 mA/g). During the first discharge cycle, rates were slightly
lower for the cell with nanoparticles of lithium titanium oxide
(7.5 mA/g versus 11 mA/g).
[0202] The cells produced with the nanoparticles had a
significantly higher capacity over the first cycle. This initial
capacity improvement can be attributed, at least in part, to a high
rate capability of the nanoparticles. However, the cells produced
with the lithium titanium oxide nanoparticle had more fade such
that by about 30 cycles the cell had similar specific capacities.
At least some of the higher fading of capacity with the
nanoparticulate Li.sub.4Ti.sub.5O.sub.12 can be attributed to the
lithium negative electrode.
[0203] 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.
* * * * *