U.S. patent application number 11/682339 was filed with the patent office on 2007-07-12 for method of making active materials for use in secondary electrochemical cells.
Invention is credited to Jeremy Barker, Aiden Bryan, Paul Burns, Richard Gover.
Application Number | 20070160519 11/682339 |
Document ID | / |
Family ID | 39816822 |
Filed Date | 2007-07-12 |
United States Patent
Application |
20070160519 |
Kind Code |
A1 |
Barker; Jeremy ; et
al. |
July 12, 2007 |
Method Of Making Active Materials For Use In Secondary
Electrochemical Cells
Abstract
The present invention provides for the preparation of an
"optimized" VPO.sub.4 phase or V--P--O/C precursor. The VPO.sub.4
precursor is an amorphous or nanocrystalline powder. The V--P--O/C
precursor is amorphous in nature and contains finely divided and
dispersed carbon. Throughout the specification it is understood
that the VPO.sub.4 precursor and the V--P--O/C precursor materials
can be used interchangeably to produce the final vanadium
phosphates, with the V--P--O/C precursor material being the
preferred precursor. The precursors can subsequently be used to
make vanadium based electroactive materials and use of such
precursor materials offers significant advantages over other
processes known for preparing vanadium phosphate compounds.
Inventors: |
Barker; Jeremy;
(Oxfordshire, GB) ; Gover; Richard;
(Worcestershire, GB) ; Burns; Paul; (Enniskillen,
GB) ; Bryan; Aiden; (Newtownabbey, GB) |
Correspondence
Address: |
VALENCE TECHNOLOGY, INC.
1889 E. MAULE AVENUE, SUITE A
LAS VEGAS
NV
89119
US
|
Family ID: |
39816822 |
Appl. No.: |
11/682339 |
Filed: |
March 6, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11277746 |
Mar 28, 2006 |
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11682339 |
Mar 6, 2007 |
|
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60729932 |
Oct 25, 2005 |
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60666132 |
Mar 28, 2005 |
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Current U.S.
Class: |
423/305 |
Current CPC
Class: |
H01M 2004/021 20130101;
H01M 4/5825 20130101; Y02E 60/10 20130101; C01B 25/455 20130101;
H01M 10/0525 20130101; H01M 10/052 20130101; C01B 25/45 20130101;
H01M 4/136 20130101 |
Class at
Publication: |
423/305 |
International
Class: |
C01B 25/37 20060101
C01B025/37 |
Claims
1. A method for making a vanadium phosphate precursor comprising
mixing V.sub.2O.sub.5 with a phosphate compound and a carbon
containing compound or a carbon precursor to form a mixture, and
heating the mixture at a temperature and for a time sufficient to
form a precursor selected from the group consisting of amorphous
V--P--O/C precursor and nanocrystalline VPO.sub.4 precursor.
2. The method according to claim 1 wherein the phosphate compound
is (NH.sub.4).sub.2HPO.sub.4 or (NH.sub.4)H.sub.2PO.sub.4.
3. The method according to claim 1 wherein the carbon is a
conductive high surface area carbon with a surface area of from
about 1 to about 1000 m.sup.2/g.
4. The method according to claim 3 wherein the carbon is selected
from carbon black; Super P, Shawinaghan black and mixtures
thereof.
5. The method according to claim 2 wherein the carbon is selected
from a graphitic carbon and organic precursor materials.
6. The method according to claim 1 wherein the mixture is heated at
a temperature in the range from about 650.degree. C. to about
900.degree. C.
7. The method according to claim 3 wherein the temperature is from
about 700.degree. C. to about 800.degree. C.
8. A method for making a vanadium phosphate compound of the
formula: A.sub.aV.sub.1-xM.sub.x(PO.sub.4).sub.dZ.sub.f. (I)
wherein A is selected from the group consisting of Li, Na, K and
mixtures thereof; a is greater than 0.1 and less than or equal to
3; x is greater than or equal to zero and less than 1; d is greater
than 0 and less than or equal to 3; M is a metal selected from the
group consisting of Al, Ti, Cr, Fe, Mn, Mo, and Nb; Z is F, Cl, or
OH: and f is greater than or equal to zero but less than or equal
to three; comprising mixing the VPO.sub.4 precursor or V--P--O/C
precursor produced according to the method of claim 1 with an
alkali metal containing compound to form a mixture and heating the
mixture at a temperature and for a time sufficient to form the
vanadium phosphate compound.
9. The method according to claim 7 wherein the mixture further
comprises a second metal containing compound.
10. The method according to claim 7 wherein the alkali metal
compound is selected from the group consisting of LiF, NaF, NaOH,
LiOH, Na.sub.2CO.sub.3 and Li.sub.3PO.sub.4.
11. The method according to claim 8 wherein the metal containing
compound comprises a metal ion of a metal selected from the group
consisting of Al, Ti, Cr, Fe, Mn, Mo and Nb.
12. The method according to claim 7 wherein the vanadium phosphate
compound produced is selected from LiVPO.sub.4,
LiV.sub.1-xAl.sub.xPO.sub.4F, Na.sub.xVPO.sub.4F.sub.x,
Li.sub.0.1Na.sub.0.9VPO.sub.4F, NaVPO.sub.4F, NaVPO.sub.4OH,
NaVPO.sub.4F, Li.sub.3V.sub.2(PO.sub.4).sub.3,
LiV.sub.0.75Al.sub.0.25PO.sub.4F, LiV.sub.0.5Al.sub.0.5PO.sub.4F,
Na.sub.1.2VPO.sub.4F.sub.1.2 and
Na.sub.3V.sub.2(PO.sub.4).sub.2F.sub.3.
13. A method for making a vanadium phosphate compound of the
formula: A.sub.aV.sub.1-xM.sub.xP.sub.2O.sub.7 (I) wherein A is
selected from the group consisting of Li, Na, K and mixtures
thereof; a is greater than 0.1 and less than or equal to 3; x is
greater than or equal to zero and less than 1; and M is a metal
selected from the group consisting of Al, Ti, Cr, Fe, Mn, Mo and
Nb; comprising mixing the VPO.sub.4 precursor or V--P--O/C
precursor produced according to the method of claim 1 with an
alkali metal containing compound to form a mixture and heating the
mixture at a temperature and for a time sufficient to form the
vanadium phosphate compound.
14. The method according to claim 7 wherein the mixture further
comprises a second metal containing compound.
15. The method according to claim 7 wherein the alkali metal
compound is selected from the group consisting of LiF, NaF, NaOH,
LiOH, Na.sub.2CO.sub.3 and Li.sub.3PO.sub.4.
16. The method according to claim 8 wherein the metal containing
compound comprises a metal ion of a metal selected from the group
consisting of Al, Ti, Cr, Fe, Mn, Mo and Nb.
17. The method according to claim 7 wherein the vanadium phosphate
compound produced is LiVP.sub.2O.sub.7.
18. A method for making a vanadium phosphate precursor comprising
mixing V.sub.2O.sub.5 with a phosphate compound and heating the
mixture in a reducing atmosphere at a temperature and for a time
sufficient to form a precursor selected from the group consisting
of amorphous V--P--O/C precursor and nanocrystalline VPO.sub.4
precursor.
19. The method according to claim 18 wherein the phosphate compound
is (NH.sub.4).sub.2HPO.sub.4 or (NH.sub.4)H.sub.2PO.sub.4.
20. The method according to claim 18 wherein the mixture
additionally comprises a conductive high surface area carbon with a
surface area of from about 1 to about 1000 m.sup.2/g.
21. The method according to claim 20 wherein the mixture
additionally comprises carbon selected from carbon black; Super P,
Shawinaghan black and mixtures thereof.
22. The method according to claim 18 wherein the mixture
additionally comprises carbon selected from a graphitic carbon and
organic precursor materials.
23. The method according to claim 18 wherein the mixture is heated
at a temperature in the range from about 650.degree. C. to about
900.degree. C.
24. The method according to claim 18 wherein the temperature is
from about 700.degree. C. to about 800.degree. C.
Description
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 11/277,746 filed Mar. 28, 2006, which claims
priority from U.S. provisional patent application 60/729,932 filed
Oct. 25, 2005, which claims priority from U.S. provisional patent
application 60/666,132 filed Mar. 28, 2005.
FIELD OF THE INVENTION
[0002] The present invention relates to the novel preparation of a
nanocrystalline VPO.sub.4 precursor and in another embodiment to an
amorphous V--P--O/C precursor (or V--P--O-carbon composite
material/precursor). The invention further relates to the use of
this VPO.sub.4 precursor or V--P--O/C precursor in methods for
making vanadium phosphate compounds. Such methods for making
vanadium phosphates are beneficial in that the methods proceed at
faster reaction rates and at lower temperatures then known methods
for making vanadium phosphates. Such precursors also produce a
purer product. The vanadium phosphate compounds so prepared are
electroactive and are useful in making electrochemical cells.
BACKGROUND OF THE INVENTION
[0003] A battery pack consists of one or more electrochemical cells
or batteries, wherein each cell typically includes a positive
electrode, a negative electrode, and an electrolyte or other
material for facilitating movement of ionic charge carriers between
the negative electrode and positive electrode. As the cell is
charged, cations migrate from the positive electrode to the
electrolyte and, concurrently, from the electrolyte to the negative
electrode. During discharge, cations migrate from the negative
electrode to the electrolyte and, concurrently, from the
electrolyte to the positive electrode.
[0004] By way of example and generally speaking, lithium ion
batteries are prepared from one or more lithium ion electrochemical
cells containing electrochemically active (electroactive)
materials. Such cells typically include, at least, a negative
electrode, a positive electrode, and an electrolyte for
facilitating movement of ionic charge carriers between the negative
and positive electrode. As the cell is charged, lithium ions are
transferred from the positive electrode to the electrolyte and,
concurrently from the electrolyte to the negative electrode. During
discharge, the lithium ions are transferred from the negative
electrode to the electrolyte and, concurrently from the electrolyte
back to the positive electrode. Thus with each charge/discharge
cycle the lithium ions are transported between the electrodes. Such
lithium ion batteries are called rechargeable lithium ion batteries
or rocking chair batteries.
[0005] The electrodes of such batteries generally include an
electroactive material having a crystal lattice structure or
framework from which ions, such as lithium ions, can be extracted
and subsequently reinserted and/or from which ions such as lithium
ions can be inserted or intercalated and subsequently extracted.
Recently a class of transition metal phosphates and mixed metal
phosphates have been developed, which have such a crystal lattice
structure. These transition metal phosphates are insertion based
compounds and allow great flexibility in the design of lithium ion
batteries.
[0006] A class of such materials is disclosed in U.S. Pat. No.
6,528,033 B1 (Barker et al.). The compounds therein are of the
general formula Li.sub.aMI.sub.bMII.sub.c(PO.sub.4).sub.d wherein
MI and MII are the same or different. MI is a metal selected from
the group consisting of Fe, Co, Ni, Mn, Cu, V, Sn, Cr and mixtures
thereof. MII is optionally present, but when present is a metal
selected from the group consisting of Mg, Ca, Zn, Sr, Pb, Cd, Sn,
Ba, Be and mixtures thereof. More specific examples of such
compounds include compounds wherein MI is vanadium and more
specifically includes Li.sub.3V.sub.2(PO.sub.4).sub.3. U.S. Pat.
No. 6,645,452 B1 (Barker et al.) further discloses electroactive
vanadium phosphates such as LiVPO.sub.4F and
LiV.sub.0.9Al.sub.0.1PO.sub.4F.
[0007] Although these compounds find use as electrochemically
active materials these materials are not always economical to
produce. Thus it would be beneficial to have a process for
preparing such intercalation materials at lower temperatures and
with faster reaction kinetics. The inventors of the present
invention have now found a method for preparing a novel VPO.sub.4
precursor and a novel V--P--O/C precursor and processes employing
such precursors to produce vanadium phosphate compounds more
economically and efficiently.
SUMMARY OF THE INVENTION
[0008] The present invention provides for the preparation of an
"optimized" VPO.sub.4 phase or V--P--O/C precursor. The VPO.sub.4
precursor is an amorphous or nanocrystalline powder. The V--P--O/C
precursor is amorphous in nature and contains finely divided and
dispersed carbon. Throughout the specification it is understood
that the VPO.sub.4 precursor and the V--P--O/C precursor materials
can be used interchangeably to produce the final vanadium
phosphates, with the V--P--O/C precursor material being the
preferred precursor. The precursors can subsequently be used to
make vanadium based electroactive materials and use of such
precursor materials offers significant advantages over other
processes known for preparing vanadium phosphate compounds.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a schematic cross-sectional diagram illustrating
the structure of a non-aqueous electrolyte cylindrical
electrochemical cell of the present invention.
[0010] FIG. 2 is a representative X-ray pattern for a sample of an
amorphous V--P--O/C sample prepared at 700.degree. C. for 4 hours
as in Example 1.
[0011] FIG. 3 is an X-ray powder pattern for a sample of
LiVPO.sub.4F for a product prepared according to Example 2.
[0012] FIG. 4 is observed, difference and calculated plot obtained
from Rietveld analysis of an optimized sample of LiVPO.sub.4F
prepared in Example 2.
[0013] FIG. 5 shows a schematic representation of the structure of
LiVPO.sub.4F projected down the c-axis.
[0014] FIG. 6 shows the first cycle current data for a
Li//LiVPO.sub.4F cell made with the LiVPO.sub.4F prepared in
Example 2.
[0015] FIG. 7 shows a representative X-ray powder patterns for
LiV.sub.1-xAl.sub.xPO.sub.4F made by the process according to
Example 3.
[0016] FIG. 8 shows the unit cell volume versus Al content for
LiV.sub.1-xAl.sub.xPO.sub.4F made by the process according to
Example 3.
[0017] FIG. 9 shows a comparison of the electrochemical response of
Li//LiVPO.sub.4F, Li//LiAl.sub.0.25V.sub.0.75PO.sub.4F and
Li//LiAl.sub.0.5V.sub.0.5PO.sub.4F cells made by the process of
Example 3.
[0018] FIG. 10 shows a representative X-ray powder pattern for
LiVP.sub.2O.sub.7 made by the process of Example 5.
[0019] FIG. 11 shows the observed, difference and calculated plots
obtained for a sample of LiVP.sub.2O.sub.7 made by the process of
Example 5.
[0020] FIG. 12 shows a schematic representation of the structure of
LiVP.sub.2O.sub.7 made by the process of Example 5.
[0021] FIG. 13 shows a first cycle constant current data for a
Li//LiVP.sub.2O.sub.7 cell.
[0022] FIG. 14 shows EVS data for a representative
Li//LiVP.sub.2O.sub.7 cell cycled between 2.5-4.7 V. Left: EVS
Voltage profile. Right: EVS Differential Capacity Profile.
[0023] FIG. 15 shows EVS data for a representative
graphite//LiVP.sub.2O.sub.7 lithium ion cell cycled between 2.5-4.6
V. The data shown is for the tenth cycle. Left: EVS Voltage
Profile. Right EVS Differential Capacity Profile.
[0024] FIG. 16 shows the life cycle data collected for
LiVP.sub.2O.sub.7//graphite cell.
[0025] FIG. 17 shows X-ray patterns for samples of
LiV.sub.1-xAl.sub.xPO.sub.4F prepared according to the process of
Example 10.
[0026] FIG. 18 shows the electrochemical results for samples of
LiV.sub.1-xAl.sub.xP.sub.2O.sub.7 prepared according to Example
10.
[0027] FIG. 19 shows a comparison of a sample of LVP prepared using
conventional known methods and prepared using the VPO.sub.4 process
according to Example 11.
[0028] FIG. 20 shows the EVS electrochemical response for LVP
sample prepared according to Example 11
[0029] FIG. 21 shows the X-ray powder pattern for the sample of
Na.sub.3V.sub.2(PO.sub.4).sub.2F.sub.3 prepared according to the
method of Example 12.
DETAILED DESCRIPTION OF THE INVENTION
[0030] Specific benefits and embodiments of the present invention
are apparent from the detailed description set forth herein below.
It should be understood, however, that the detailed description and
specific examples, while indicating embodiments among those
preferred, are intended for purposes of illustration only and are
not intended to limit the scope of the invention.
[0031] The following is a list of some of the definitions of
various terms used herein:
[0032] As used herein "battery" refers to a device comprising one
or more electrochemical cells for the production of electricity.
Each electrochemical cell comprises an anode, a cathode and an
electrolyte.
[0033] As used herein the terms "anode" and "cathode" refer to the
electrodes at which oxidation and reduction occur, respectively,
during battery discharge. During charging of the battery, the sites
of oxidation and reduction are reversed.
[0034] As used herein the terms "nominal formula" or "nominal
general formula" refer to the fact that the relative proportion of
atomic species may vary slightly on the order of 2 percent to 5
percent, or more typically, 1 percent to 3 percent.
[0035] As used herein the words "preferred" and "preferably" refer
to embodiments of the invention that afford certain benefits under
certain circumstances. Further the recitation of one or more
preferred embodiments are not useful and is not intended to exclude
other embodiments from the scope of the invention.
[0036] Referring to FIG. 1, a secondary electrochemical cell 10
having an electrode active material described herein below as
nominal general formula (I), is illustrated. The cell 10 includes a
spirally coiled or wound electrode assembly 12 enclosed in a sealed
container, preferably a rigid cylindrical casing 14. The electrode
assembly 12 includes: a positive electrode 16 consisting of, among
other things, an electrode active material described herein below;
a counter negative electrode 18; and a separator 20 interposed
between the first and second electrodes 16, 18. The separator 20 is
preferably an electrically insulating, ionically conductive
microporous film, and composed of a polymeric material selected
from the group consisting of polyethylene, polyethylene oxide,
polyacrylonitrile and polyvinylidene fluoride, polymethyl
methacrylate, polysiloxane, copolymers thereof, and admixtures
thereof.
[0037] Each electrode 16, 18 includes a current collector 22 and
24, respectively, for providing electrical communication between
the electrodes 16, 18 and an external load. Each current collector
22, 24 is a foil or grid of an electrically conductive metal such
as iron, copper, aluminum, titanium, nickel, stainless steel, or
the like, having a thickness of between 5 .mu.m and 100 .mu.m,
preferably 5 .mu.m and 20 .mu.m. Optionally, the current collector
may be treated with an oxide-removing agent such as a mild acid and
the like, and coated with an electrically conductive coating for
inhibiting the formation of electrically insulating oxides on the
surface of the current collector 22, 24. Examples of suitable
coatings include polymeric materials comprising a homogenously
dispersed electrically conductive material (e.g. carbon), such
polymeric materials including: acrylics including acrylic acid and
methacrylic acids and esters, including poly (ethylene-co-acrylic
acid); vinylic materials including poly(vinyl acetate) and
poly(vinylidene fluoride-co-hexafluoropropylene); polyesters
including poly(adipic acid-co-ethylene glycol); polyurethanes;
fluoroelastomers; and mixtures thereof.
[0038] The positive electrode 16 further includes a positive
electrode film 26 formed on at least one side of the positive
electrode current collector 22, preferably both sides of the
positive electrode current collector 22, each film 26 having a
thickness of between 10 .mu.m and 150 .mu.m, preferably between 25
.mu.m an 125 .mu.m, in order to realize the optimal capacity for
the cell 10. The positive electrode film 26 is preferably composed
of between 80% and 99% by weight of an electrode active material
described herein below as general formula (I), between 1% and 10%
by weight binder, and between 1% and 10% by weight electrically
conductive agent.
[0039] Suitable binders include: polyacrylic acid;
carboxymethylcellulose; diacetylcellulose; hydroxypropylcellulose;
polyethylene; polypropylene; ethylene-propylene-diene copolymer;
polytetrafluoroethylene; polyvinylidene fluoride; styrene-butadiene
rubber; tetrafluoroethylene-hexafluoropropylene copolymer;
polyvinyl alcohol; polyvinyl chloride; polyvinyl pyrrolidone;
tetrafluoroethylene-perfluoroalkylvinyl ether copolymer; vinylidene
fluoride-hexafluoropropylene copolymer; vinylidene
fluoride-chlorotrifluoroethylene copolymer;
ethylenetetrafluoroethylene copolymer; polychlorotrifluoroethylene;
vinylidene fluoride-pentafluoropropylene copolymer;
propylene-tetrafluoroethylene copolymer;
ethylene-chlorotrifluoroethylene copolymer; vinylidene
fluoride-hexafluoropropylene-tetrafluoroethylene copolymer;
vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene
copolymer; ethylene-acrylic acid copolymer; ethylene-methacrylic
acid copolymer; ethylene-methyl acrylate copolymer; ethylene-methyl
methacrylate copolymer; styrene-butadiene rubber; fluorinated
rubber; polybutadiene; and admixtures thereof. Of these materials,
most preferred are polyvinylidene fluoride and
polytetrafluoroethylene.
[0040] Suitable electrically conductive agents include: natural
graphite (e.g. flaky graphite, and the like); manufactured
graphite; carbon blacks such as acetylene black, Ketzen black,
channel black, furnace black, lamp black, thermal black, and the
like; conductive fibers such as carbon fibers and metallic fibers;
metal powders such as carbon fluoride, copper, nickel, and the
like; and organic conductive materials such as polyphenylene
derivatives.
[0041] The negative electrode 18 is formed of a negative electrode
film 28 formed on at least one side of the negative electrode
current collector 24, preferably both sides of the negative
electrode current collector 24. The negative electrode film 28 is
composed of between 80% and 95% of an intercalation material,
between 2% and 10% by weight binder, and (optionally) between 1%
and 10% by weight of an electrically conductive agent.
[0042] Intercalation materials suitable herein include: transition
metal oxides, metal chalcogenides, carbons (e.g. graphite), and
mixtures thereof capable of intercalating the alkali metal-ions
present in the electrolyte in the electrochemical cell's nascent
state.
[0043] In one embodiment, the intercalation material is selected
from the group consisting of crystalline graphite and amorphous
graphite, and mixtures thereof, each such graphite having one or
more of the following properties: a lattice interplane (002)
d-value (d.sub.(002)) obtained by X-ray diffraction of between 3.35
.ANG. to 3.34 .ANG., inclusive (3.35
.ANG..ltoreq.d.sub.(002).ltoreq.3.34 .ANG.), preferably 3.354 .ANG.
to 3.370 .ANG., inclusive (3.354
.ANG..ltoreq.d.sub.(002).ltoreq.3.370 .ANG.; a crystallite size
(L.sub.c) in the c-axis direction obtained by X-ray diffraction of
at least 200 .ANG., inclusive (L.sub.c.gtoreq.200 .ANG.),
preferably between 200 .ANG. and 1,000 .ANG., inclusive (200
.ANG..ltoreq.L.sub.c.ltoreq.1,000 .ANG.); an average particle
diameter (P.sub.d) of between 1 .mu.m to 30 .mu.m, inclusive (1
.mu.m .ltoreq.P.sub.d.ltoreq.30 .mu.m); a specific surface (SA)
area of between 0.5 m.sup.2/g to 50 m.sup.2/g, inclusive (0.5
m.sup.2/g.ltoreq.SA.ltoreq.50 m.sup.2/g); and a true density
(.rho.) of between 1.9 g/cm.sup.3 to 2.25 g/cm.sup.3, inclusive
(1.9 g/cm.sup.3.ltoreq..rho..ltoreq.2.25 g/cm.sup.3).
[0044] Referring again to FIG. 1, to ensure that the electrodes 16,
18 do not come into electrical contact with one another, in the
event the electrodes 16, 18 become offset during the winding
operation during manufacture, the separator 20 "overhangs" or
extends a width "a" beyond each edge of the negative electrode 18.
In one embodiment, 50 .mu.m.ltoreq.a.ltoreq.2,000 .mu.m. To ensure
alkali metal does not plate on the edges of the negative electrode
18 during charging, the negative electrode 18 "overhangs" or
extends a width "b" beyond each edge of the positive electrode 16.
In one embodiment, 50 .mu.m.ltoreq.b.ltoreq.2,000 .mu.m.
[0045] The cylindrical casing 14 includes a cylindrical body member
30 having a closed end 32 in electrical communication with the
negative electrode 18 via a negative electrode lead 34, and an open
end defined by crimped edge 36. In operation, the cylindrical body
member 30, and more particularly the closed end 32, is electrically
conductive and provides electrical communication between the
negative electrode 18 and an external load (not illustrated). An
insulating member 38 is interposed between the spirally coiled or
wound electrode assembly 12 and the closed end 32.
[0046] A positive terminal subassembly 40 in electrical
communication with the positive electrode 16 via a positive
electrode lead 42 provides electrical communication between the
positive electrode 16 and the external load (not illustrated).
Preferably, the positive terminal subassembly 40 is adapted to
sever electrical communication between the positive electrode 16
and an external load/charging device in the event of an overcharge
condition (e.g. by way of positive temperature coefficient (PTC)
element), elevated temperature and/or in the event of excess gas
generation within the cylindrical casing 14. Suitable positive
terminal assemblies 40 are disclosed in U.S. Pat. No. 6,632,572 to
Iwaizono, et al., issued Oct. 14, 2003; and U.S. Pat. No. 6,667,132
to Okochi, et al., issued Dec. 23, 2003. A gasket member 42
sealingly engages the upper portion of the cylindrical body member
30 to the positive terminal subassembly 40.
[0047] A non-aqueous electrolyte (not shown) is provided for
transferring ionic charge carriers between the positive electrode
16 and the negative electrode 18 during charge and discharge of the
electrochemical cell 10. The electrolyte includes a non-aqueous
solvent and an alkali metal salt dissolved therein capable of
forming a stable SEI layer on the negative electrode (most
preferably, a lithium salt). In the electrochemical cell's nascent
state (namely, before the cell undergoes cycling), the non-aqueous
electrolyte contains one or more metal-ion charge carriers.
[0048] Suitable solvents include: a cyclic carbonate such as
ethylene carbonate, propylene carbonate, butylene carbonate or
vinylene carbonate; a non-cyclic carbonate such as dimethyl
carbonate, diethyl carbonate, ethyl methyl carbonate or dipropyl
carbonate; an aliphatic carboxylic acid ester such as methyl
formate, methyl acetate, methyl propionate or ethyl propionate; a
.gamma.-lactone such as .gamma.-butyrolactone; a non-cyclic ether
such as 1,2-dimethoxyethane, 1,2-diethoxyethane or
ethoxymethoxyethane; a cyclic ether such as tetrahydrofuran or
2-methyltetrahydrofuran; an organic aprotic solvent such as
dimethylsulfoxide, 1,3-dioxolane, formamide, acetamide,
dimethylformamide, dioxolane, acetonitrile, propylnitrile,
nitromethane, ethyl monoglyme, phospheric acid triester,
trimethoxymethane, a dioxolane derivative, sulfolane,
methylsulfolane, 1,3-dimethyl-2-imidazolidinone,
3-methyl-2-oxazolidinone a propylene carbonate derivative, a
tetrahydrofuran derivative, ethyl ether, 1,3-propanesultone,
anisole, dimethylsulfoxide and N-methylpyrrolidone; and mixtures
thereof. A mixture of a cyclic carbonate and a non-cyclic carbonate
or a mixture of a cyclic carbonate, a non-cyclic carbonate and an
aliphatic carboxylic acid ester, are preferred.
[0049] Suitable alkali metal salts, particularly lithium salts,
include: LiClO.sub.4; LiBF.sub.4; LiPF.sub.6; LiAlCl.sub.4;
LiSbF.sub.6; LiSCN; LiCF.sub.3SO.sub.3; LiCF.sub.3CO.sub.2;
Li(CF.sub.3SO.sub.2).sub.2; LiAsF.sub.6; LiN(CF.sub.3SO2).sub.2;
LiB.sub.10Cl.sub.10; a lithium lower aliphatic carboxylate; LiCl;
LiBr; Lil; a chloroboran of lithium; lithium tetraphenylborate;
lithium imides; LiBOB (lithium bis(oxalate)borate) and mixtures
thereof. Preferably, the electrolyte contains at least
LiPF.sub.6.
[0050] One embodiment of the invention involves the production of a
nanocrystalline and/or amorphous VPO.sub.4. This material can be
used a precursor for preparing various vanadium based products.
This material is very reactive and allows for the preparation of
various vanadium based products at low temperatures and with very
fast kinetics. Additionally this VPO.sub.4 is useful as a precursor
of vanadium based products in that other processes for making the
vanadium based products may cause production of unwanted impurity
phases, such as V.sub.2O.sub.3, in the vanadium based products.
[0051] In another embodiment the invention involves the production
of a amorphous V--P--O/C precursor with no "definite" composition
(see FIG. 2). This V--P--O/C precursor has the correct ratio of V
and PO.sub.4 to make the final product (e.g. LiVPO.sub.4F), is
close to X-ray amorphous (see FIG. 2) and it contains finely
divided and dispersed carbon. This material can be used a precursor
for preparing various vanadium based products This material is very
reactive and allows for the preparation of various vanadium based
products at low temperatures and with very fast kinetics.
Additionally this V--P--O/C precursor is useful as a precursor of
vanadium based products in that other processes for making the
vanadium based products may cause production of unwanted impurity
phases, such as V.sub.2O.sub.3, in the vanadium based products.
[0052] It is understood that the VPO.sub.4 and V--P--O/C precursor
materials can be used interchangeably in the reactions described
herein. The V--P--O/C precursor is the preferred precursor. Thus
where it is stated that VPO.sub.4 is used the V--P--O/C precursor
could alternately be used and vice versa. Alternatively, either
precursor may be referred to as a vanadium phosphate precursor.
[0053] The vanadium phosphate precursor is made for example by
mixing vanadium pentoxide (V.sub.2O.sub.5), ammonium hydrogen
phosphate [(NH.sub.4).sub.2HPO.sub.4 or (NH.sub.4)H.sub.2PO.sub.4]
and a source of carbon, such as Enasco carbon. The mixture is then
milled and/or micronized (i.e. some form of high energy
mixing/homogenizing), pelletized and heated at a temperature in the
range from about 400.degree. C. to about 900.degree. C. Preferably
the milled mixture is heated in the temperature range from about
500.degree. C. to about 800.degree. C. and more preferably from
about 600.degree. C. to about 750.degree. C. The mixture is heated
from about 30 minutes to about 16 hours and more preferably from
about 1 to about 8 hours.
[0054] The amorphous V--P--O/C precursors may be produced at
temperatures from 300-800.degree. C. and more preferably at about
600.degree. C. Reaction of these preferred amorphous V--P--O/C
precursors with appropriate alkali metal compounds result in
improved vanadium phosphate products which can be produced at lower
temperatures than when using the crystalline VPO.sub.4
precursors.
[0055] The reaction proceeds according to the following equations:
0.5
V.sub.2O.sub.5+(NH.sub.4).sub.2HPO.sub.4+carbon.fwdarw.VPO.sub.4+2NH.sub.-
3+1.5 H.sub.2O+CO or 0.5
V.sub.2O.sub.5+(NH.sub.4)H.sub.2PO.sub.4+carbon.fwdarw.VPO.sub.4+NH.sub.3-
+1.5 H.sub.2O.
[0056] Alternatively other vanadium containing compounds such as
V.sub.2O.sub.3, VO.sub.2, NH.sub.4VO.sub.3 and the like can be used
in the place of the V.sub.2O.sub.5. If lithium products are the
desired end products LiVO.sub.3 and the like may also be employed
in place of the V.sub.2O.sub.3. Likewise, alternatively other
phosphate sources such as P.sub.2O.sub.5, H.sub.3PO.sub.4 and the
like can be used in place of the ammonium phosphate starting
materials.
[0057] In one aspect, the source of carbon is provided by elemental
carbon, preferably in particulate form such as graphites, amorphous
carbon, carbon blacks and the like. In another aspect, the source
of carbon may also be provided by an organic precursor material, or
by a mixture of elemental carbon and organic precursor material.
The organic precursor material will also be referred to in this
application as an organic material. The organic material or organic
precursor material is one that is capable of forming a
decomposition product that contains carbon. The carbon is formed in
situ.
[0058] Alternatively or in addition, the source of carbon may be
provided by an organic material. The organic material is
characterized as containing carbon and at least one other element,
preferably hydrogen. The organic material generally forms a
decomposition product, referred to herein as a carbonaceous
material, upon heating under the conditions of the reaction.
[0059] The organic precursor material may be any organic material
capable of undergoing pyrolysis or carbonization, or any other
decomposition process that leads to a carbonaceous material rich in
carbon. Such precursors include in general any organic material,
i.e., compounds characterized by containing carbon and at least one
other element. Although the organic material may be a perhalo
compound containing essentially no carbon-hydrogen bonds, typically
the organic materials contain carbon and hydrogen. Other elements,
such as without limitation, halogens, oxygen, nitrogen, phosphorus,
and sulfur, may be present in the organic material, as long as they
do not significantly interfere with the decomposition process. One
example of a preferred organic material is coke, which contains
mostly carbon and hydrogen. Other precursors include, without
limitation, organic hydrocarbons, alcohols, esters, ketones,
aldehydes, carboxylic acids, sulfonates, and ethers. Preferred
precursors include the above species containing aromatic rings,
especially the aromatic hydrocarbons such as tars, pitches, and
other petroleum products or fractions. As used here, hydrocarbon
refers to an organic compound made up of carbon and hydrogen, and
containing no significant amounts of other elements. Hydrocarbons
may contain impurities having some heteroatoms. Such impurities
might result, for example, from partial oxidation of a hydrocarbon
or incomplete separation of a hydrocarbon from a reaction mixture
or natural source such as petroleum.
[0060] Other organic precursor materials include sugars and other
carbohydrates, including derivatives and polymers. Examples of
polymers include, without limitation, starch, cellulose, and their
ether or ester derivatives. Other derivatives include, without
limitation, the partially reduced and partially oxidized
carbohydrates discussed below. On heating, carbohydrates readily
decompose to form carbon and water. The term carbohydrates as used
here encompasses the D-, L-, and DL-forms, as well as mixtures, and
includes material from natural or synthetic sources.
[0061] In one sense as used in the invention, carbohydrates are
organic materials that can be written with molecular formula
(C).sub.m (H.sub.2O).sub.n, where m and n are integers. For simple
hexose or pentose sugars, m and n are equal to each other.
Non-limiting examples of hexoses of formula C.sub.6H.sub.12O.sub.6
include allose, altose, glucose, mannose, gulose, inose, galactose,
talose, sorbose, tagatose, and fructose. Pentoses of formula
C.sub.5H.sub.10O.sub.5 are represented by, without limitation,
ribose, arabinose, and xylose. Tetroses include erythrose and
threose, while glyceric aldehyde is a triose. Other carbohydrates
include the two-ring sugars (di-saccharides) of general formula
C.sub.12H.sub.22O.sub.11. Examples include, without limitation,
sucrose, maltose, lactose, trehalose, gentiobiose, cellobiose, and
melibiose. Three-ring (trisaccharides such as raffinose) and higher
oligomeric and polymer carbohydrates may also be used. Non-limiting
examples include starch and cellulose. As noted above, the
carbohydrates readily decompose to carbon and water when heated to
a sufficiently high temperature. The water of decomposition tends
to turn to steam under the reaction conditions and volatilize.
[0062] It will be appreciated that other materials will also tend
to readily decompose to H.sub.2O and a material very rich in
carbon. Such materials are also intended to be included in the term
"carbohydrate" as used in the invention. Such materials include
slightly reduced carbohydrates such as, without limitation,
glycerol, sorbitol, mannitol, iditol, dulcitol, talitol, arabitol,
xylitol, and adonitol, as well as "slightly oxidized" carbohydrates
such as, without limitation, gluconic, mannonic, glucuronic,
galacturonic, mannuronic, saccharic, manosaccharic, ido-saccharic,
mucic, talo-mucic, and allo-mucic acids. The formula of the
slightly oxidized and the slightly reduced carbohydrates is similar
to that of the carbohydrates.
[0063] A preferred carbohydrate is sucrose. Under the reaction
conditions, sucrose melts at about 150-180.degree. C. The liquid
melt tends to distribute itself among the starting materials. At
temperatures above about 450.degree. C., sucrose and other
carbohydrates decompose to form carbon and water. The as-decomposed
carbon powder is in the form of fresh amorphous fine particles with
high surface area and high reactivity.
[0064] The organic precursor material may also be an organic
polymer. Organic polymers include without limitation, polyolefins
such as polyethylene and polypropylene, butadiene polymers,
isoprene polymers, vinyl alcohol polymers, furfuryl alcohol
polymers, styrene polymers including polystyrene,
polystyrene-polybutadiene and the like, divinylbenzene polymers,
naphthalene polymers, phenol condensation products including those
obtained by reaction with aldehyde, polyacrylonitrile, polyvinyl
acetate, as well as cellulose starch and esters and ethers thereof
described above.
[0065] In some embodiments, the organic precursor material is a
solid available in particulate form. Particulate materials may be
combined with the other particulate starting materials and reacted
by heating according to the methods described above.
[0066] In other embodiments, the organic precursor material may be
a liquid. In such cases, the liquid precursor material is combined
with the other particulate starting materials to form a mixture.
The mixture is heated, whereupon the organic material forms a
carbonaceous material in situ. The liquid precursor materials may
also advantageously serve or function as a binder in the starting
material mixture as noted above.
[0067] In an alternative embodiment of the invention the vanadium
phosphate precursor is made for example by mixing vanadium
pentoxide (V.sub.2O.sub.5), ammonium hydrogen phosphate
[(NH.sub.4).sub.2HPO.sub.4 or (NH.sub.4)H.sub.2PO.sub.4]. The
mixture is then milled and/or micronized (i.e. some form of high
energy mixing/homogenizing), pelletized and heated at a temperature
in the range from about 400.degree. C. to about 900.degree. C. in
the presence of reducing gas or gases. Non-limiting examples or
reducing gases include hydrogen, methane, ammonia and carbon
monoxide. The reducing atmosphere may be provided as pure reducing
gas, or as mixtures of reducing gas with other gases. Non-limiting
examples of reducing atmosphere mixtures include hydrogen-argon,
hydrogen-nitrogen, carbon monoxide-hydrogen, carbon monoxide-argon,
and the like. The reducing gas may but need not be provided in
molar excess. The reducing gas may be used in partial pressures
from about 0.01 atmosphere up to super-atmospheric, depending on
such factors as the size of the sample, the volume of the heating
chamber, and the excess of gas, if any, required for the
reaction
[0068] In an alternate embodiment the reaction is carried out in a
reducing atmosphere in the presence of a reductant. Such reductant
includes, without limitation carbon and organic precursor materials
as discussed above. Such reducing atmosphere, includes without
limitation, the reducing gases and mixtures thereof discussed
above.
[0069] In one embodiment of the invention the vanadium phosphate
precursor is mixed with an alkali metal containing compound and
optionally with another metal containing compound to produce alkali
metal vanadium phosphate compounds. By way of example alkali metal
containing compounds include NaF, LiF, LiH.sub.2PO.sub.4, NaOH,
Na.sub.2CO.sub.3, Li.sub.3PO.sub.4 and the like and mixtures
thereof. If the desired end product is a fluorophosphate (e.g.
NaVPO.sub.4F, LiVPO.sub.4F) suitable precursors can include
NH.sub.4F and the like together with an appropriate alkali ion
salt. Preferred alkali metal containing compounds are compounds
containing Na or Li and the more preferred alkali metal containing
compounds contain Li. The optional metal containing compounds are
compounds containing a metal ion selected from the group consisting
of Al, Ti, Cr, Fe Mn, Mo, Nb and the like. Examples of such metal
containing compounds include for example AlPO.sub.4,
Fe.sub.2O.sub.3, Mn.sub.2O.sub.3, Fe.sub.3O.sub.4, FeO, MnO.sub.2,
MnO, CrPO.sub.4, FePO.sub.4 MnPO.sub.4, aluminum hydroxide,
aluminum oxide, aluminum carbonate, Cr.sub.2O.sub.3,
Nb.sub.2O.sub.5 and the like.
[0070] The vanadium phosphate precursors are then reacted with an
appropriate alkali metal according to, for example the following
reactions: 3 LiH.sub.2PO.sub.4+2
VPO.sub.4.fwdarw.Li.sub.3V.sub.2(PO.sub.4).sub.3+3H.sub.2O or
VPO.sub.4+LiF.fwdarw.LiVPO.sub.4F or 3 NaF+2
VPO.sub.4.fwdarw.Na.sub.3V.sub.2(PO.sub.4).sub.2F.sub.3.
[0071] The alkali metal compound is a compound of lithium, sodium,
or potassium. The alkali metal compound serves as a source of
alkali metal ion in particulate form. Preferred alkali metal
compounds are sodium compounds and lithium compounds. Examples of
compounds include, without limitation, carbonates, metal oxides,
hydroxides, sulfates, aluminates, phosphates and silicates.
Examples of lithium compounds thus include, without limitation,
lithium carbonates, lithium metal oxides, lithium mixed metal
oxides, lithium hydroxides, lithium aluminates, and lithium
silicates, while analogous sodium compounds are also preferred. A
preferred lithium compound is lithium carbonate. Sodium carbonate
and sodium hydroxide are preferred sodium compounds.
[0072] Typically the VPO.sub.4 precursor, alkali metal containing
compound and optional other metal containing compound are milled
and then pelletized. The mixture is then heated at a temperature
from about 500.degree. C. to about 900.degree. C. More preferably
the mixture is heated from about 500.degree. C. to about
800.degree. C. and most preferably from about 600.degree. C. to
about 750.degree. C. The mixture is heated for about 30 minutes to
about 16 hours and more preferably from about 1 to about 8
hours.
[0073] The reaction produces electrode active compounds represented
by the nominal general formula (I):
A.sub.aV.sub.1-xM.sub.x(PO.sub.4).sub.dZ.sub.f. (I) wherein A is
selected from the group consisting of Li, Na, K and mixtures
thereof; [0074] a is greater than 0.1 and less than or equal to 3;
[0075] x is zero or less than 1; [0076] d is greater than 0 and
less than or equal to 3 [0077] M is a metal selected from the group
consisting of Al, Ti, Cr, Fe, Mn, Mo, Nb and mixtures thereof;
[0078] Z is F, Cl, or OH: [0079] and f is greater than or equal to
0 but less than or equal to 3.
[0080] Examples of such compounds include but are not limited to
LiVPO.sub.4, LiV.sub.1-xAl.sub.xPO.sub.4F,
Na.sub.xVPO.sub.4F.sub.x, Li.sub.0.1Na.sub.0.9VPO.sub.4F,
NaVPO.sub.4F, NaVPO.sub.4OH, NaVPO.sub.4F,
Li.sub.3V.sub.2(PO.sub.4).sub.3, LiV.sub.0.75Al.sub.0.25PO.sub.4F,
LiV.sub.0.5Al.sub.0.5PO.sub.4F, Na.sub.1.2VPO.sub.4F.sub.1.2 and
Na.sub.3V.sub.2(PO.sub.4).sub.2F.sub.3, and the like.
[0081] In another embodiment of the invention the reaction produces
electrode active compounds represented by the nominal general
formula (I): A.sub.aV.sub.1-xM.sub.xP.sub.2O.sub.7 (I) [0082]
wherein A is selected from the group consisting of Li, Na, K and
mixtures thereof; [0083] a is greater than 0.1 and less than or
equal to 3; [0084] x is greater than or equal 0 and less than 1;
and [0085] M is a metal selected from the group consisting of Al,
Ti, Cr, Cr, Fe, Mn, Mo, Nb and mixtures thereof. An example of such
electrode active material includes, but is not limited to
LiVP.sub.2O.sub.7.
[0086] The electrode active materials described herein are in their
nascent or as-synthesized state, prior to undergoing cycling in an
electrochemical cell. The components of the electrode active
material are selected so as to maintain electroneutrality of the
electrode active material. The stoichiometric values of one or more
elements of the composition may take on non-integer values.
[0087] In all embodiments described herein, moiety Z (when
provided) is selected from the group consisting of OH (hydroxyl), a
halogen, or mixtures thereof. In one embodiment, Z is selected from
the group consisting of OH, F (Fluorine), Cl (Chlorine), and
mixtures thereof. In another embodiment, Z is OH. In another
embodiment, Z is F, or a mixture of F with OH or Cl.
[0088] Typically for electrochemical testing, composite electrodes
were fabricated using 84-wt % active material, 6-wt % Super P
(conductive carbon) and 10-wt % PVdf-HFP co-polymer (Elf Atochem)
binder. The electrolyte comprised a 1 M LiPF.sub.6 solution in
ethylene carbonate/dimethyl carbonate (2:1 by weight) while a dried
glass fiber filter (Whatman, Grade GF/A) was used as the electrode
separator. A commercially available crystalline graphite or lithium
metal foil were used as the anode active material. High-resolution
electrochemical measurements were performed using the
Electrochemical Voltage Spectroscopy (EVS) technique. (J. Barker,
Electrochim. Acta, 40, 1603 (1995)). EVS is a voltage step method,
which provides a high resolution approximation to the open circuit
voltage curve for the electrochemical system under investigation.
Cycling tests of the hybrid-ion cells were performed using a
commercial battery cycler (Maccor Inc., Tulsa, Okla., USA).
[0089] The following non-limiting examples illustrate the
compositions and methods of the present invention.
EXAMPLE 1
Preparation of VPO.sub.4
[0090] VPO.sub.4 was prepared according to the following reaction:
1/2 V.sub.2O.sub.5+(NH.sub.4).sub.2HPO.sub.4+1.0
C.fwdarw.VPO.sub.4+2 NH.sub.3+3/2 H.sub.2O+CO 9.1 g V.sub.2O.sub.5,
13.2 g of (NH.sub.4).sub.2HPO.sub.4 and 1.32 g of carbon (10% mass
excess) were used. Carbon was added to the reaction mixture so that
the V.sup.5+ in the V.sub.2O.sub.5 was reduced to V.sup.3+ in the
product which is an example of carbothermal reduction. The excess
carbon in the product helps act as a conducting agent in the
vanadium phosphate electroactive materials produced therefrom,
which improves the electrochemical properties of such electroactive
materials.
[0091] It has been found that it is necessary to use a homogenous
starting material. This can be achieved using high energy milling
methods, which can include ball milling and micronizing. The sample
prepared herein were prepared using McCrone micronizers to obtain
the starting materials.
[0092] The VPO.sub.4 materials prepared herein were prepared at a
number of different temperatures in the range from about
650.degree. C. to about 900.degree. C. The samples prepared at
higher temperatures contained V.sub.2O.sub.3 as an impurity. Such
materials would be unsuitable as precursors since V.sub.2O.sub.3 is
known to be detrimental to the electrochemical performance in Li
ion cells. It has been found that preparing these materials at low
temperatures, typically about 700.degree. C. for about 4 to about
16 hours under a flowing argon atmosphere can be used effectively
for the preparation of a number of precursor materials. The
precursor materials on removal from the furnace range from dark
brown to black in color. The color is dependent on the amount of
carbon added in the initial reaction mixture.
[0093] FIG. 2 is a typical X-ray powder pattern obtained for a
sample of V--P--O/C precursor made at 700.degree. for 4 hours. The
powder pattern of these materials prepared at low temperature
generally have a "featureless" powder pattern, which can be
interpreted as being due to either the material being amorphous or
that the obtained crystallites are very small nanoparticles.
EXAMPLE 2
Preparation of LiVPO.sub.4F using VPO.sub.4
[0094] LiVPO.sub.4 was prepared according to the following
reaction: LiF+VPO.sub.4.fwdarw.LiVPO.sub.4F The LiF (2.6 g) and
VPO.sub.4 (1.46 g) were mixed and micronized. The amount of LiF
added is dependent on the amount of residual carbon present in the
VPO.sub.4. The stoichiometric amount of LiF is added based on the
above reaction. An allowance can be made for the amount of residual
carbon left over from the V--P--O/C synthesis. This is normally
about 3 weight percent. The mixture was then heated in the
temperature range of about 600.degree. to about 700.degree. C. for
up to about 1 hour. At temperatures in excess of 700.degree. C., it
is believed that VF.sub.3 sublimation occurs which leads to the
formation of Li.sub.3V.sub.2(PO.sub.4).sub.3 (LVP-nasicon).
[0095] FIG. 3 shows an example of a powder pattern obtained for a
sample of LiVPO.sub.4F. Refinement of the XRD data for the
LiVPO.sub.4F samples was carried out using the Rietveld method. H.
M. Rietveld, J. Appl. Crystallograph, 2, (1969) 65. R. A. Young in
"The Rietveld Method", Chapter 1, Oxford Science Publications. A.
C. Larsen and R. B. Von Dreele, Los Alamos Laboratory Report,
NO-LA-U-86-746 (1987). The X-ray data can be satisfactorily refined
using a structural model based on either Tavorite, LiFePO.sub.4OH
(U.S. Pat. No. 6,387,568 Barker et al.) or Amblygonite,
LiAlPO.sub.4F (Groat et al, American Mineralogist, 88, 195 (2003).
The X-ray data for the LiVPO.sub.4F samples derived from the
optimized synthesis conditions for this process favor the
Amblygonite structural model as the most likely structure of this
model. (Such optimized conditions being V--P--O/C prepared at
700.degree. C., followed by reaction with LiF at 700.degree. C. to
produce LiVPO.sub.4).
[0096] FIG. 4 shows the fit obtained for the LiVPO.sub.4F sample
using the Rietveld analysis. The refined cell parameters are given
as space group P-1: a=5.16727(13) .ANG., b=5.30590(13) .ANG.,
c=7.28964(19) .ANG., .alpha.=108.9108(14).degree.,
.beta.=107.2137(13).degree., .gamma.=98.4002(16).degree. and cell
volume=174.007(8) .ANG..sup.3; with fitting statistics being
R.sub.wp 11.08%, R.sub.p=8.05% and x=2.352.
[0097] FIG. 5 shows a schematic representation (along the c axis)
of the LiVPO.sub.4F based on the Amblygonite structural model. The
LiVPO.sub.4F structure comprises a three dimensional framework
being built from [PO.sub.4] tetrahedral and [VO.sub.4F.sub.2]
octahedral with the oxygen atoms shared between the PO.sub.4 and
VO.sub.4F.sub.2. This model predicts the presence of two distinct
crystallographic sites for alkali ions which explains the
electrochemical lithium extraction behavior exhibited by this
material.
[0098] An electrode is made with 84% of the active material, 6% of
Super P conductive carbon, and 10% poly vinylidene difluoride. A
cell with that electrode as cathode and lithium anode is
constructed with an electrolyte comprising 1 M LiPF.sub.6 dissolved
in 2:1 by weight mixture of ethylene carbonate:dimethyl
carbonate.
[0099] FIG. 6 shows the first cycle constant current data obtained
for the cell built using the sample of LiVPO.sub.4F. A slight
inflection is seen in the data during the charge process, which is
related to preferential depopulation of one of the Li sites within
the structure. No such feature is observed during the discharge
process, indicating that during reinsertion of the Li neither of
the sites is preferred. This observation is clearly supported by
the observation of two peaks in the differential capacity plot
obtained during EVS measurement. Long term cycling of this material
shows good electrochemical properties.
EXAMPLE 3
[0100] An electrode active material comprising
LiV.sub.1-xAl.sub.xPO.sub.4F was made according to the following
reaction scheme: (1-x)VPO.sub.4+x AlPO.sub.4+LiF
.fwdarw.LiV.sub.1-xAl.sub.xPO.sub.4F
[0101] The LiF, VPO.sub.4 and AIPO.sub.4 were mixed and micronized
in the required amounts. If for example x=0.2 0.8 VPO.sub.4+0.2
AlPO.sub.4+LiF.fwdarw.LiVo.sub.0.8Al.sub.0.2PO.sub.4F Then 1.167 g
of VPO.sub.4 were mixed with 0.244 g AlPO.sub.4 and 0.259 g LiF.
The mixture was then heated in the temperature range
600-700.degree. C. for up to 1 hour.
[0102] An electrode is made with 84% of the active material, 6% of
Super P conductive carbon, and 10% poly vinylidene difluoride. A
cell with that electrode as cathode and a lithium anode is
constructed with an electrolyte comprising 1 M LiPF.sub.6 dissolved
in 2:1 by weight mixture of ethylene carbonate:dimethyl
carbonate.
[0103] FIG. 7 shows the X-ray powder patterns for samples of
LiV.sub.1-xAl.sub.xPO.sub.4F. The results shown in FIG. 7 show that
high quality samples can be prepared relatively easily.
[0104] FIG. 8 is a plot of Al content versus unit cell volume,
obtained from Rietveld analysis of several samples. The plot
clearly shows a linear relationship between Al content and the unit
cell volume which is consistent with Vegards law, i.e. formation of
a solid solution series between the V and Al.
[0105] Varying the amount of Al in a sample makes it possible to
vary the operating voltage of the sample. FIG. 9 shows a comparison
of the electrochemical response of samples containing varying
amounts of Al. Addition of more Al to a sample has the effect of
reducing the overvoltage (i.e. voltage polarization) and is thought
to be related to the increase in substitutionial disorder of the
material. The addition of Al on the V sites upsets the ordering
(V-V-etc) of the transition metal. This will affect the resultant
voltage characteristics to some extent. However, as Al is
electrochemically inactive it has the effect of reducing the
overall capacity of the material. Life cycling data suggests that
the Al doped samples have a lower fade rate then observed with
LiVPO.sub.4F.
EXAMPLE 4
[0106] An electrode active material comprising
Na.sub.1.2VPO.sub.4F.sub.1.2 was made as follows. In a first step,
a metal phosphate was made by carbothermal reduction of a metal
oxide, here exemplified by vanadium pentoxide. The overall reaction
scheme of the carbothermal reduction is as follows.
0.5V.sub.2O.sub.5+NH.sub.4H.sub.2PO.sub.4+C.fwdarw.VPO.sub.4+NH.sub.3+1.5-
H.sub.2O+CO 9.1 grams of V.sub.2O.sub.5, 11.5 grams of
NH.sub.4H.sub.2PO.sub.4 and 1.2 grams of carbon (10% excess) are
used. The precursors were premixed using a mortar and pestle and
then pelletized. The pellet was transferred to an oven equipped
with a flowing argon atmosphere. The sample was heated at a ramp
rate of 2.degree. per minute to an ultimate temperature of
300.degree. C. and maintained at this temperature for three hours.
The sample was cooled to room temperature, removed from the oven,
recovered, re-mixed and repelletized. The pellet is transferred to
a furnace with an argon atmosphere. The sample is heated at a ramp
rate of 2.degree. per minute to an ultimate temperature 750.degree.
C. and maintained at this temperature for 8 hours.
[0107] In a second step, the vanadium phosphate made in the first
step was reacted with an alkali metal halide, exemplified by sodium
fluoride, according to the following reaction scheme.
xNaF+VPO.sub.4.fwdarw.Na.sub.xVPO.sub.4F.sub.x 14.6 grams of
VPO.sub.4 and 4.2 grams of NaF were used. The precursors are
pre-mixed using a mortar and pestle and then pelletized. The pellet
was transferred to an oven equipped with a flowing argon
atmosphere. The sample was heated at a ramp rate of 2.degree. per
minute to an ultimate temperature of 750.degree. C. and maintained
at this temperature for an hour. The sample was cooled and removed
from the furnace.
[0108] To make Na.sub.1.2VPO.sub.4F.sub.1.2, the reaction is
repeated with a 20% mass excess of sodium fluoride over the
previous reaction. The precursors were pre-mixed using a mortar and
pestle and pelletized as before. The sample was heated to an
ultimate temperature of 700.degree. C. and maintained at this
temperature for 15 minutes. The sample was cooled and removed from
the oven. There is only a small weight loss during reaction,
indicating almost full incorporation of the NaF. To make an active
material of formula Na.sub.1.5VPO.sub.4F.sub.1.5 the reaction is
repeated with an approximate 50% mass excess of sodium fluoride
over the first reaction. The sample is heated at 700.degree. C. for
15 minutes, cooled, and removed from the oven.
[0109] An electrode is made with 84% of the active material, 6% of
Super P conductive carbon, and 10% poly vinylidene difluoride. A
cell with that electrode as cathode and lithium foil as anode is
constructed with an electrolyte comprising 1 M LiPF.sub.6 dissolved
in 2:1 by weight mixture of ethylene carbonate:dimethyl
carbonate.
EXAMPLE 5
[0110] An electrode active material comprising LiVP.sub.2O.sub.7
was made according to the following reaction scheme.
LiH.sub.2PO.sub.4+VPO.sub.4.fwdarw.LiVP.sub.2O.sub.7+H.sub.2O
LiH.sub.2PO.sub.4 (10.39 g) and VPO.sub.4 (14.59 g) were used. The
precursors were mixed using a mortar and pestle and then
pelletized. The pellet was transferred to an oven equipped with a
flowing argon atmosphere. The sample was heated at a ramp rate of
2.degree. per minute to an ultimate temperature of 750.degree. C.
and maintained at this temperature for an hour. It has been found
that this material can be prepared in temperatures ranging from
about 650.degree. C. to about 850.degree. C. The sample is cooled
and removed from the furnace.
[0111] An electrode is made with 84% of the active material, 6% of
Super P conductive carbon, and 10% poly vinylidene difluoride. A
cell with that electrode as cathode and carbon intercalation anode
is constructed with an electrolyte comprising 1 M LiPF.sub.6
dissolved in 2:1 by weight mixture of ethylene carbonate:dimethyl
carbonate.
[0112] FIG. 10 is a representative X-ray powder pattern for
LiVP.sub.2O.sub.7. The structure of this material has been examined
using the Rietveld method using the model presented by Rousse.
Rousse et al., Int. J. Inorg. Mat., 3, 881 (2001). The obtained fit
is presented in FIG. 11. The refined unit cell lattice parameters
are: a=4.8211(2) .ANG., b=8.1283(3) .ANG., c=6.9404(3) .ANG.,
.alpha.=90.degree., .beta.=108.949(2).degree., .gamma.=90.degree.,
volume=257.24(2) .ANG..sup.3 with R.sub.wp=12.97%, R.sub.p=9.23%
and x.sup.2=1.30.
[0113] The structure of LiVP.sub.2O.sub.7 can be described as a 3-D
framework of corner sharing VO.sub.6 octahedra and P.sub.2O.sub.7
groups. This framework arrangement provides tunnels in which Li
ions are coordinated tetrahedrally, as shown in FIG. 12.
[0114] Previous studies by Uebou and Wurm have shown that this
material has relatively poor electrochemical properties, with
discharge capacities in the region of 50 mAh/g observed at a very
low rate (typically a very low rate). Uebou et al., Solid State
Ionics, 148, 323, (2002). Wurm et al., Chem. Mater., 14, 2701,
(2002). The present inventors have found that by producing a
composite of this diphosphate and a high surface area carbon, there
is a noticeable improvement in the electrochemical properties. The
properties are shown in FIG. 13.
[0115] The data in FIG. 13 shows a discharge capacity in the region
of about 68 MAh/g. Taking into account the residual carbon this
discharge capacity has a value closer to about 71 mAh/g. Although
this would appear to be only a modest improvement over that
reported by Uebou and Wum, these experiments were performed at a
rate in the region of C/15. It is believed that some of the
irreversibility is due to the upper voltage limit used in this
experiment.
[0116] FIG. 14 shows the results of an EVS experiment performed
using voltage limits of 2.5 to 4.7 volts (versus Li). The
reversible specific capacity for LiVP.sub.2O.sub.7 is 93 mAh/g. It
was noted however, that the capacity increased slowly over the
first ten cycles, reaching 101 mAh/g after the tenth cycle.
Examination of the differential capacity versus cell voltage plot
shows that this system works with relatively low polarization. The
differential capacity plot shows some evidence of decomposition at
voltages greater than approximately 4.35 volts.
[0117] Similarly, good results have been obtained in Li ion cells,
with EVS results after 10 cycles shown in FIG. 15. It can be seen
therefrom that there is a decrease in observed cell polarization.
FIG. 16 shows the results of life cycle experiments performed with
this material.
EXAMPLE 6
[0118] An electrode active material comprising
Li.sub.0.1Na.sub.0.9VPO.sub.4F was made according to the following
reaction scheme.
xLiF+(1-x)NaF+VPO.sub.4.fwdarw.Li.sub.xNa.sub.1-xVPO.sub.4F As an
alternative to using alkali fluorides, a reaction between VPO.sub.4
and NH.sub.4F and a mixture of Li.sub.2CO.sub.3 and
Na.sub.2CO.sub.3 may also be used.
[0119] To make Li.sub.0.1Na.sub.0.9VPO.sub.4F, 1.459 grams
VPO.sub.4, 0.026 grams of LiF, and 0.378 grams of NaF were
premixed, pelletized, placed in an oven and heated to an ultimate
temperature of 700.degree. C. The temperature is maintained for
fifty minutes after which the sample is cooled to room temperature
and removed from the oven. To make
Li.sub.0.95Na.sub.0.05VPO.sub.4F, 1.459 grams of VPO.sub.4, 0.246
grams of LiF, and 0.021 grams of NaF are mixed together and heated
in an oven as in the previous step. An electrode is made with 84%
of the active material, 6% of Super P conductive carbon, and 10%
poly vinylidene difluoride. A cell with that electrode as cathode
and carbon intercalation anode is constructed with an electrolyte
comprising 1 M LiPF.sub.6 dissolved in 2:1 by weight mixture of
ethylene carbonate:dimethyl carbonate.
EXAMPLE 7
[0120] An electrode active material comprising NaVPO.sub.4F is made
hydrothermally according to the following reaction scheme.
NaF+VPO.sub.4.fwdarw.NaVPO.sub.4F 1.49 grams of VPO.sub.4 and 1.42
grams of NaF are premixed with approximately 20 milliliters of
deionized water, transferred and sealed in a Parr Model 4744 acid
digestion bomb, which is a Teflon lined stainless steel
hydrothermal reaction vessel. The bomb is placed in an oven and
heated at a ramp rate of 5.degree. per minute to an ultimate
temperature of 250.degree. C. to create an internal pressure and
maintained at this temperature for forty-eight hours. The sample is
slowly cooled to room temperature and removed from the furnace for
analysis. The product sample is washed repeatedly with deionized
water to remove unreacted impurities. Then the sample is dried in
an oven equipped with argon gas flow at 250.degree. C. for one
hour. An electrode is made with 84% of the active material, 6% of
Super P conductive carbon, and 10% poly vinylidene difluoride. A
cell with that electrode as cathode and carbon intercalation anode
is constructed with an electrolyte comprising 1 M LiPF.sub.6
dissolved in 2:1 by weight mixture of ethylene carbonate:dimethyl
carbonate.
EXAMPLE 8
[0121] An electrode active material of formula NaVPO.sub.4OH is
made according to the following reaction scheme.
NaOH+VPO.sub.4.fwdarw.NaVPO.sub.4OH
[0122] In this Example, the reaction of the Example 7 is repeated,
except that an appropriate molar amount of sodium hydroxide is used
instead of sodium fluoride. The reaction is carried out
hydrothermally as in Example 7. The hydroxyl group is incorporated
into the active material at the relatively low temperature of
reaction. An electrode is made with 84% of the active material, 6%
of Super P conductive carbon, and 10% poly vinylidene difluoride. A
cell with that electrode as cathode and carbon intercalation anode
is constructed with an electrolyte comprising 1 M LiPF.sub.6
dissolved in 2:1 by weight mixture of ethylene carbonate:dimethyl
carbonate.
EXAMPLE 9
[0123] An electrode active material comprising NaVPO.sub.4F is made
according to the following reaction scheme.
0.5Na.sub.2CO.sub.3+NH.sub.4F+VPO.sub.4.fwdarw.NaVPO.sub.4F+NH.sub.3+0.5C-
O.sub.2+0.5H.sub.2O
[0124] 1.23 grams of VPO.sub.4, 0.31 grams of NH.sub.4F, and 0.45
grams Na.sub.2CO.sub.3 are premixed with approximately 20
milliliters of deionized water and transferred and sealed in a Parr
Model 4744 acid digestion bomb, which is a Teflon lined stainless
steel reaction vessel. The bomb is placed in an oven and heated to
an ultimate temperature of 250.degree. C. and maintained at this
temperature for forty-eight hours. The sample is cooled to room
temperature and removed for analysis. The sample is washed
repeatedly with the deionized water to remove unreacted impurities
and thereafter is dried in an argon atmosphere at 250.degree. C.
for an hour. An electrode is made with 84% of the active material,
6% of Super P conductive carbon, and 10% poly vinylidene
difluoride. A cell with that electrode as cathode and carbon
intercalation anode is constructed with an electrolyte comprising 1
M LiPF.sub.6 dissolved in 2:1 by weight mixture of ethylene
carbonate:dimethyl carbonate.
EXAMPLE 10
[0125] Electrode active materials comprising compounds of the
formula LiV.sub.1-xAl.sub.xPO.sub.4 were made according to the
following reaction scheme: (1-x) VPO.sub.4+x
AlPO.sub.4+LiH.sub.2PO.sub.4.fwdarw.LiV.sub.1-xAl.sub.xP.sub.2O.sub.7+H.s-
ub.2O
[0126] The precursors were mixed using a mortar and pestle and then
palletized. The pellet was transferred to an oven equipped with a
flowing argon atmosphere. The samples were heated at a ramp rate of
2.degree. per minute to an ultimate temperature of about
650.degree. C. to about 850.degree. C. and maintained at these
temperatures for about 4 to about 8 hours. The sample is cooled and
removed from the furnace. An electrode is made with 84% of the
active material, 6% of Super P conductive carbon, and 10%
polyvinylidene difluoride. A cell with that electrode as cathode
and lithium anode is constructed with an electrolyte comprising 1M
LiPF.sub.6 dissolved in 2:1 by weight ethylene carbonate to
dimethyl carbonate is constructed and tested.
[0127] Al.sup.3+ is electrochemically inactive and therefore
reduces the amount of Li that can be extracted. Thus many of the
samples prepared were lower Al content samples, typically in the
range of 5-15% Al doping. The X-ray patterns for a selection of
samples so prepared are shown in FIG. 17.
[0128] The electrochemical properties of the samples so prepared
are shown in FIG. 18.
EXAMPLE 11
[0129] An electrode active material comprising
Li.sub.3V.sub.2(PO.sub.4).sub.3 was made according to the following
reaction scheme.
Li.sub.3PO.sub.4+2VPO.sub.4.fwdarw.Li.sub.3V.sub.2(PO.sub.4).sub.3
LiPO.sub.4 (11.58 g) and VPO.sub.4 (29.18 g) were used. The
precursors were mixed using a mortar and pestle and then
pelletized. The pellet was transferred to an oven equipped with a
flowing argon atmosphere. The samples were heated at a ramp rate of
2.degree. per minute to an ultimate temperature of about
650.degree. C. to about 850.degree. C. and preferably 700 to
750.degree. C. and maintained at these temperatures for about 1 to
about 8 hours. The sample is cooled and removed from the
furnace.
[0130] FIG. 19 shows a representative X-ray pattern of a sample
prepared as above.
[0131] An electrode is made with 84% of the active material, 6% of
Super P conductive carbon, and 10% poly vinylidene difluoride. A
cell with that electrode as cathode and a lithium anode is
constructed with an electrolyte comprising 1 M LiPF.sub.6 dissolved
in 2:1 by weight mixture of ethylene carbonate:dimethyl
carbonate.
[0132] FIG. 20 shows the electrochemical properties of the
sample.
EXAMPLE 12
[0133] An electrode active material comprising
Na.sub.3V.sub.2(PO.sub.4).sub.2F.sub.3 is made as follows. First, a
VPO.sub.4 precursor is made according to the following reaction
scheme. V.sub.2O.sub.5+2 (NH.sub.4).sub.2HPO.sub.4+2 C.fwdarw.2
VPO.sub.4+4 NH.sub.3+3 H.sub.2O+2 CO A mixture of 18.2 g (0.1 mol)
of V.sub.2O.sub.5, 26.4 g (0.2 mol) of (NH.sub.4).sub.2HPO.sub.4,
and 2.64 g (0.2 mol+10% mass excess) of elemental carbon was made,
using a mortar and pestle. The mixture was pelletized, and
transferred to a box oven equipped with an argon gas flow. The
mixture was heated to a temperature of about 350.degree. C., and
maintained at this temperature for 3 hours. The mixture was then
heated to a temperature of about 750.degree. C., and maintained at
this temperature for 8 hours. The product is then cooled to ambient
temperature (about 21.degree. C.).
[0134] Na.sub.3V.sub.2(PO.sub.4).sub.2F.sub.3 was then made from
the VPO.sub.4 precursor. The material was made according to the
following reaction scheme. 2 VPO.sub.4+3
NaF.fwdarw.Na.sub.3V.sub.2(PO.sub.4).sub.2F.sub.3 A mixture of
VPO.sub.4 (2.918 g) and NaF (1.26 g) was made, using a mortar and
pestle. The mixture was pelletized, and transferred to a
temperature-controlled tube furnace equipped with an argon gas
flow. The mixture is heated at a ramp rate of about
2.degree./minute to an ultimate temperature of about 750.degree. C.
for 1 hour Temperatures can be in the region of 700-800.degree. C.
for these samples and can be heated in this region for about one to
about four hours. The product is then cooled to ambient temperature
(about 20.degree. C.). A representative X-ray powder pattern is
shown in FIG. 21 X-ray powder diffraction analysis for the
Na.sub.3V.sub.2(PO.sub.4).sub.2F.sub.3 material indicated the
material to be single phase with a tetragonal structure (space
group P42/mnm). The unit cell parameters (a=9.0304(5) .ANG.,
c=10.6891(9) .ANG.) were calculated from a least squares refinement
procedure, in fair agreement with the structural analysis for
Na.sub.3V.sub.2(PO.sub.4).sub.2F.sub.3 described by Meins et al.,
J. Solid State Chem., 148, 260, (1999). (i.e. a=9.047(2) .ANG.,
c=10.705(2) .ANG.).
EXAMPLE 13
[0135] 0.5
V.sub.2O.sub.5+(NH.sub.4).sub.2HPO.sub.4+C.fwdarw.VPO.sub.4+NH.sub.3+1.5
H.sub.2O+CO
[0136] Vanadium oxide (V.sub.2O.sub.5; 9.10 g), diammonium hydrogen
phosphate (13.2 g) and elemental carbon (1.32 g, 10% mass excess)
were weighed and poured into a micronising pot. The materials were
then micronised for 15 minutes. This process step has the dual
purpose of providing intimate mixing and dispersion of the raw
materials to produce a homogenous mixture and reducing particles
size of the material due to the grinding/milling action. After
micronising, the resulting powder was pressed to form a pellet. The
pellet was placed in a crucible and placed in a tube furnace. The
pellet was fired at 700.degree. C. at a ramp rate of 2.degree.
C./minute with a 16 hour dwell under an inert atmosphere. After
firing, the pellet was broken up and ground to produce a powder.
FIG. 23 shows the X-rd trace for the resulting VPO.sub.4. The trace
shows that the VPO.sub.4 is an amorphous V--P--O/C precursor.
VPO.sub.4+LiF.fwdarw.LiVPO.sub.4F
[0137] The VPO.sub.4 (1.46 g) precursor so obtained was then
micronised for 15 minutes with LiF (0.26 g). After micronising, the
resultant powder was pressed to form a pellet was placed in a
crucible, sealed by a second crucible and placed in a tube furnace.
The pellet is fired at 700.degree. C. at a ramp rate of 2.degree.
C./minute with a one hour dwell under an inert atmosphere. After
firing, the pellet was broken up and ground to produce the final
LiVPO.sub.4F material. FIG. 24 shows the Xrd trace for the
resulting LiVPO.sub.4F.
[0138] The examples and other embodiments described herein are
exemplary and not intended to be limiting in describing the full
scope of compositions and methods of this invention. Equivalent
changes, modifications and variations of specific embodiments,
materials, compositions and methods may be made within the scope of
the present invention, with substantially similar results.
* * * * *