U.S. patent application number 11/968783 was filed with the patent office on 2008-05-01 for synthesis of cathode active materials.
Invention is credited to Biying Huang, Haitao Huang, M. Yazid Saidi, Jeffrey Swoyer.
Application Number | 20080099720 11/968783 |
Document ID | / |
Family ID | 35375547 |
Filed Date | 2008-05-01 |
United States Patent
Application |
20080099720 |
Kind Code |
A1 |
Huang; Biying ; et
al. |
May 1, 2008 |
SYNTHESIS OF CATHODE ACTIVE MATERIALS
Abstract
The present invention relates to a method for preparing an
electroactive metal polyanion or a mixed metal polyanion comprising
forming a slurry comprising a polymeric material, a solvent, a
polyanion source or alkali metal polyanion source and at least one
metal ion source; heating said slurry at a temperature and for a
time sufficient to remove the solvent and form an essentially dried
mixture; and heating said mixture at a temperature and for a time
sufficient to produce an electroactive metal polyanion or
electroactive mixed metal polyanion. The electrochemically active
materials so produced are useful in making electrodes and
batteries.
Inventors: |
Huang; Biying; (Las Vegas,
NV) ; Swoyer; Jeffrey; (Henderson, NV) ;
Saidi; M. Yazid; (Henderson, NV) ; Huang; Haitao;
(Henderson, NV) |
Correspondence
Address: |
VALENCE TECHNOLOGY, INC.
1889 E. MAULE AVENUE, SUITE A
LAS VEGAS
NV
89119
US
|
Family ID: |
35375547 |
Appl. No.: |
11/968783 |
Filed: |
January 3, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10850003 |
May 20, 2004 |
7338647 |
|
|
11968783 |
Jan 3, 2008 |
|
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Current U.S.
Class: |
252/182.1 ;
423/306 |
Current CPC
Class: |
H01M 4/485 20130101;
C01B 25/45 20130101; H01M 4/5825 20130101; H01M 4/5815 20130101;
H01M 4/622 20130101; Y02E 60/10 20130101; H01M 4/364 20130101 |
Class at
Publication: |
252/182.1 ;
423/306 |
International
Class: |
C01B 25/30 20060101
C01B025/30; H01M 4/48 20060101 H01M004/48 |
Claims
1. An electrode active material of the formula
A.sub.aMI.sub.bMII.sub.c(XY.sub.4).sub.dZ.sub.e wherein: (i) A
comprises at least one alkali metal selected from the group
consisting of Li, Na, K, and mixtures thereof and 0<a=6: (ii) MI
comprises a metal ion of a metal selected from the group consisting
of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Si, Sn, Pb and mixtures
thereof and 0<b=4; (iii) MII comprises a metal ion of a metal
selected from the group consisting of Be, Mg, Ca, Sr, Ba, Zn, Cd,
Ge, Sc, Y, B, Al, Ga and mixtures thereof and 0=c=4; (iv) XY.sub.4
is selected from the group consisting of X'[O.sub.4-x,Y'.sub.x],
X'[O.sub.4-yY'.sub.2y], X''S.sub.4, [X.sub.z''',X'.sub.1-z]O.sub.4
and mixtures thereof wherein: (a) X' and X''' are each
independently selected from the group consisting of P, As, Sb, Si,
Ge, S and mixtures thereof; (b) X'' is selected from the group
consisting of P, As, Sb, Si, Ge, V and mixtures thereof; (c) Y' is
selected from the group consisting of a halogen, and mixtures
thereof; and (d) 0=x=3, 0<y<2, and 0<z<1; and (i) Z is
selected from the group consisting of OH, a halogen and mixtures
thereof, and 0<d=6; wherein A, M, X, Y, Z, a, b, x, y, z, c and
d are selected so as to maintain electroneutrality of the material
made by a process comprising the steps of: forming a mixture
comprising a solvent having a boiling point, a polyanion source, a
source of at least one metal ion, an alkali metal and a polymeric
material wherein the polymeric material forms a solution with the
solvent without substantial phase separation; heating the mixture
at a temperature greater than the boiling point of the solvent for
a period of time sufficient to remove substantially all of the
solvent to produce an essentially dried mixture; heating the dried
mixture at a temperature and for a period of time sufficient to
produce the electrode active material.
2. The electrode active material according to claim 1 wherein the
mixture or dried mixture produced in the process further comprises
a carbon source.
3. The electrode active material according to claim 1 wherein
during the heating steps the polymeric material decomposes to form
an electron conductive network throughout the electrode active
material.
4. The electrode active material according to claim 1 wherein the
solvent used in the process is selected from the group consisting
of water, deionized water, PC, EC, DMF, DME, THF, BL, NMP, DMSO and
mixtures thereof.
5. The electrode active material according to claim 4, wherein the
polyanion source used in the process is polyanion-containing
compound selected from the group consisting of a
PO.sub.4-containing compound, a SiO.sub.4 containing compound, a
GeO.sub.4-containing compound, a VO.sub.4-containing compound, an
AsO.sub.4-containing compound, a SbO.sub.4-containing compound, and
a SO.sub.4-containing compound.
6. The electrode active material according to claim 5 wherein the
polyanion-containing compound used in the process is a
PO.sub.4-containing compound.
7. The electrode active material according to claim 6 wherein the
PO.sub.4-containing compound used in the process is selected from
the group consisting of diammonium hydrogen phosphate, ammonium
dihydrogen phosphate, lithium dihydrogen phosphate and mixtures
thereof.
8. The electrode active material according to claim 1 wherein the
source of at least one metal ion used in the process is a compound
of a metal selected from the group consisting of Ti, V, Cr, Mn, Fe,
Co, Ni, Cu, Mo, Si, Sn, Pb and mixtures thereof.
9. The electrode active material according to claim 1 wherein the
electrode active material produced is lithium vanadium
phosphate.
10. The electrode active material according to claim 1 wherein the
material produced is of the formula LiFe.sub.1-xMg.sub.xPO.sub.4
wherein x is from about 0.01 to about 0.1.
11. A cathode comprising the electrode active material of claim
1.
12. A battery comprising a cathode according to claim 11.
Description
[0001] This application is a divisional of and claims priority from
U.S. Ser. No. 10/850,003, filed May 20, 2004, now allowed.
FIELD OF THE INVENTION
[0002] The present invention relates to the synthesis of
electroactive materials for use in batteries, more specifically to
cathode active materials for use in lithium ion batteries.
BACKGROUND OF THE INVENTION
[0003] The proliferation of portable electronic devices such as
cell phones and laptop computers has lead to an increased demand
for high capacity, long endurance light weight batteries. Because
of this alkali metal batteries, especially lithium ion batteries,
have become a useful and desirable energy source. Lithium metal,
sodium metal, and magnesium metal batteries are well known and
desirable energy sources.
[0004] By way of example and generally speaking, lithium batteries
are prepared from one or more lithium 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 rechargeable batteries are
called rechargeable lithium ion batteries or rocking chair
batteries.
[0005] The electrodes of such batteries generally include an
electrochemically active material having a crystal lattice
structure or framework from which ions, such as lithium ions, can
be extracted and subsequently reinserted and/or permit ions such as
lithium ions to 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 like their oxide based counterparts. The
transition metal phosphates and mixed metal phosphates allow great
flexibility in the design of lithium ion batteries.
[0006] Recently, three-dimensional structured compounds comprising
polyanions such as (SO.sub.4).sup.n-, (PO.sub.4).sup.n-,
(AsO.sub.4).sup.n-, and the like, have been proposed as viable
alternatives to oxide based electrode materials such as
LiM.sub.xO.sub.y. A class of such materials is disclosed in U.S.
Pat. No. 6,528,003 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,
Ti, Cr and mixtures thereof. MII is optionally present, but when
present is selected from the group consisting of Mg, Ca, Zn, Sr,
Pb, Cd, Sn, Ba, Be, and mixtures thereof. More specific examples of
such polyanion based materials include the olivine compounds such
as LiMPO.sub.4, wherein M.dbd.Mn, Fe, Co and the like. Other
examples of such polyanion based materials include the NASICON
compounds such as Li.sub.3M.sub.2(PO.sub.4).sub.3, and the
like.
[0007] Although these compounds find use as electrochemically
active materials useful for producing electrodes these materials
are not always economical to produce, they may afford insufficient
voltage, have insufficient charge capacity or exhibit low ionic
conductivity. The present invention provides an economical,
reproducible and efficient method for producing metal phosphates
and mixed metal phosphates with good electrochemical properties
which make them useful for producing electrodes and in particular
cathodes.
SUMMARY OF THE INVENTION
[0008] The present invention relates to a method for preparing an
electroactive metal polyanion or a mixed metal polyanion comprising
forming a slurry comprising a polymeric material, a solvent, a
polyanion source or alkali metal polyanion source and at least one
metal ion source; heating said slurry at a temperature and for a
time sufficient to remove the solvent and form an essentially dried
mixture; and heating said mixture at a temperature and for a time
sufficient to produce an electroactive metal polyanion or
electroactive mixed metal polyanion. In a preferred embodiment the
present invention relates to a method for preparing a metal
polyanion or a mixed metal polyanion which comprises dissolving a
polymeric material in a solvent to form a first solution, adding a
polyanion source or alternatively an alkali metal polyanion source
to the first solution while stirring to form a first slurry, adding
a source of at least one metal ion to said first slurry while
stirring to form a second slurry, heating said second slurry at a
temperature and for a time sufficient to remove the solvent to form
an essentially dried mixture, then heating said mixture at a
temperature and for a time sufficient to produce an electroactive
metal polyanion or an electroactive mixed metal polyanion. In an
alternative embodiment the present invention relates to a method
for preparing a metal polyanion or a mixed metal polyanion which
comprises mixing a polymeric material with a polyanion source or
alternatively an alkali metal polyanion source and a source of at
least one metal ion to produce a fine mixture and heating the
mixture to a temperature higher than the melting point of the
polymeric material, milling the resulting material and then heating
the milled material. It is another object of the invention to
provide electrochemically active materials produced by said
methods. The electrochemically active materials so produced are
useful in making electrodes and batteries.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 shows the XRD of the material produced in Example
1.
[0010] FIG. 2 shows the voltage vs. time profile of the polymeric
LVP produced according to Example 1.
[0011] FIG. 3 shows the cycling behavior and voltage profile of the
polymeric LVP produced according to Example 1 at C/2.
[0012] FIG. 4 shows the XRD of the material produced according to
Example 2.
[0013] FIG. 5 shows the voltage vs. time profile of the polymeric
LVP produced according to Example 2.
[0014] FIG. 6 shows the cycling behavior and voltage profile of the
polymeric LVP produced according to Example 2 at C/2.
[0015] FIG. 7 shows the XRD of the material produced according to
Example 3.
[0016] FIG. 8 shows the cycling behavior of the polymeric LVP
produced according to Example 3 at a current rate of C/2.
[0017] FIG. 9 shows the XRD of the material produced according to
Example 4.
[0018] FIG. 10 shows the XRD of the material produced according to
Example 5.
[0019] FIG. 11 shows the cycling behavior of the material produced
according to Example 5 at a current rate of C/2.
[0020] FIG. 12 shows the XRD of the material produced according to
Example 6
[0021] FIG. 13 shows the cycling behavior of the material produced
according to Example 6 at a current rate of C/2.
[0022] FIG. 14 shows the cycling behavior of the polymeric LVP
produced according to Example 7 at a current rate of C/2.
[0023] FIG. 15 shows the cycling behavior of the polymeric LVP
produced according to Example 8 at a current rate of C/2.
DETAILED DESCRIPTION
[0024] The present invention relates to methods for preparing
electroactive metal polyanions and mixed metal polyanions and in
particular to methods for preparing metal phosphates and mixed
metal phosphates. In another embodiment the present invention
relates to electrochemically active materials produced by such
methods, electrodes produced from such electroactive materials and
batteries which contain such electrodes.
[0025] Metal phosphates, and mixed metal phosphates and in
particular lithiated metal and mixed metal phosphates have recently
been introduced as electrode active materials for ion batteries and
in particular lithium ion batteries. These metal phosphates and
mixed metal phosphates are insertion based compounds. What is meant
by insertion is that such materials have a crystal lattice
structure or framework from which ions, and in particular lithium
ions, can be extracted and subsequently reinserted and/or permit
ions to be inserted and subsequently extracted.
[0026] The transition metal phosphates allow for great flexibility
in the design of batteries, especially lithium ion batteries.
Simply by changing the identity of the transition metal allows for
regulation of voltage and specific capacity of the active
materials. Examples of such transition metal phosphate cathode
materials include such compounds of the nominal general formulae
LiFePO.sub.4, Li.sub.3V.sub.2(PO.sub.4).sub.3 and
LiFe.sub.1-xMg.sub.xPO.sub.4 as disclosed in U.S. Pat. No.
6,528,033 B1 (Barker et al, hereinafter referred to as the '033
patent) issued Mar. 4, 2003.
[0027] A class of compounds having the general formula
Li.sub.aMI.sub.bMII.sub.c(PO.sub.4).sub.d wherein MI and MII are
the same or different are disclosed in U.S. Pat. No. 6,528,003 B1
(Barker et al.). MI is a metal selected from the group consisting
of Fe, Co, Ni, Mn, Cu, V, Sn, Ti, Pb, Si, Cr and mixtures thereof.
MII is optionally present, but when present is selected from the
group consisting of Mg, Ca, Zn, Sr, Pb, Cd, Sn, Ba, Be, and
mixtures thereof. It is disclosed therein, for example, that
LiFePO.sub.4 can be prepared by mixing the reactants
Fe.sub.2O.sub.3, Li.sub.2CO.sub.3, (NH.sub.4).sub.2HPO.sub.4 and
carbon and heating said mixture in an inert atmosphere. The carbon
is present in an amount sufficient to reduce the oxidation state of
at least one metal ion of the starting materials without full
reduction to the elemental state. This process is beneficial in
that it employs the relatively inexpensive material
Fe.sub.2O.sub.3. Previous methods for preparing LiFePO.sub.4
required the use of the more expensive Fe.sup.2+ salts, such as
oxalate, acetate or FeO.
[0028] U.S. Pat. No. 6,528,033 B1 also discloses that
LiFe.sub.1-xMg.sub.xPO.sub.4 can be prepared using Fe.sub.2O.sub.3.
LiFe.sub.1-xMg.sub.xPO.sub.4 is prepared by mixing the reactants
LiH.sub.2PO.sub.4, Fe.sub.2O.sub.3, Mg(OH).sub.2 and carbon and
heating said reaction mixture in an inert atmosphere. The carbon
again is present in an amount sufficient to reduce the oxidation
state of at least one metal ion of the starting materials without
full reduction to the elemental state. This process is also
economical in that it employs Fe.sub.2O.sub.3 instead of the more
expensive Fe.sup.2+ salts.
[0029] It is also disclosed in U.S. Pat. No. 6,528,033 B1 that
Li.sub.3V.sub.2(PO.sub.4).sub.3 (lithium vanadium phosphate) can be
prepared by ball milling V.sub.2O.sub.5, Li.sub.2CO.sub.3,
(NH.sub.4).sub.2HPO.sub.4 and carbon, and then pelletizing the
resulting powder. The pellet is then heated to 300.degree. C. to
remove CO.sub.2 from the LiCO.sub.3 and to remove the NH.sub.2. The
pellet is then powderized and repelletized. The new pellet is then
heated at 850.degree. C. for 8 hours to produce the desired
electrochemically active product.
[0030] It has been found that when making lithium vanadium
phosphate by the method of the '033 patent that problems result
from the dry ball mixing method. The dry ball-mill mixing method on
a larger production scale sometimes results in an incomplete
reaction of the starting materials. When the incomplete reaction
occurs and the product so produced is used in a cell it produces a
cell with poor cycle performance. The method on a large scale also
resulted in poor reproducibility of the product formed.
[0031] Additionally, it has been found that when lithium vanadium
phosphate and LiFe.sub.1-xMg.sub.xPO.sub.4 prepared using the
methods of the '033 patent on a larger scale are used in the
preparation of phosphate cathodes it results in phosphate cathodes
with high resistivity. The lithium vanadium phosphate and
LiFe.sub.1-xMg.sub.xPO.sub.4 powders produced by the method of the
'033 patent on a large scale also exhibit a low tap density.
[0032] It has now surprisingly been found these classes of
compounds, and compounds similar to those disclosed in U.S. Pat.
No. 6,528,033 B1 can be prepared in a beneficial manner to produce
materials with high electronic conductivity and an excellent cycle
life with superior reversible capacity. The methods of the present
invention employ a polymeric material which is capable of forming a
solution with the solvent and acts a phase separation inhibitor in
either a wet mix or dry mix method. The polymeric material also
acts to form a conductive network throughout the metal polyanions
and mixed metal polyanions produced by the process of the present
invention. It has now also been found that materials so produced
exhibit good electronic conductivity when used as the active
materials in electrodes, and preferably in cathodes.
[0033] In one embodiment of the invention a metal polyanion or
mixed metal polyanion is produced by a wet mix method. The process
comprises forming a mixture comprising a solvent having a boiling
point, together with a polymeric material, a polyanion source and a
source of at least one metal ion and heating the mixture so formed
at a temperature greater than the boiling point of the solvent for
a period of time sufficient to remove substantially all the solvent
to produce an essentially dry mixture, and heating the dried
mixture so obtained to produce an electroactive metal polyanion or
an electroactive mixed metal polyanion. The polyanion source and
polymeric material are preferably capable of forming a solution in
the solvent without substantial phase separation with the
solvent.
[0034] In a preferred embodiment the present invention relates to a
method for preparing a metal polyanion or a mixed metal polyanion
which comprises dissolving a polymeric material in a solvent to
form a first solution, adding a polyanion source or alternatively
an alkali metal polyanion source to the first solution while
stirring to form a first slurry, adding a source of at least one
metal ion to said first slurry while stirring to form a second
slurry, heating said second slurry at a temperature and for a time
sufficient to form an essentially dried mixture, then heating said
mixture at a temperature and for a time sufficient to produce an
electroactive metal polyanion or an electroactive mixed metal
polyanion.
[0035] By way of further example, the first step of a preferred
process comprises dissolving a polymeric material, in a solvent to
form a first solution. The solvent can be any volatile solvent that
can dissolve the polymeric material. Preferably, the solvent is a
volatile solvent having a boiling point of less than about
300.degree. C., preferably less than 200.degree. C. and more
preferably less than 120.degree. C. In a preferred embodiment the
solvent is water. A polyanion source (or an alkali metal polyanion
source) is added to the first solution while stirring to form a
first slurry. A source of at least one metal ion is then added to
the first slurry to form a second slurry. Said second slurry is
then heated at a temperature greater than the boiling point of the
solvent to produce an essentially dried mixture. The dried mixture
is then ball milled and heated to produce a metal phosphate or
mixed metal phosphate material with high electronic
conductivity.
[0036] It is understood and one skilled in the art would recognize
that although the preferred embodiment described above, states the
order in which the polymeric material, the polyanion source and the
metal ion are added to form the slurry that the polymeric material,
the polyanion source and the metal ion can be added to the solvent
in any order. For example, the polyanion source and the metal ion
source can be added to the solvent and then the polymeric material
can be added. Alternatively, the metal ion source can be added to
the solvent, then the polymeric material and then the polyanion
source. The polymer can be added to the solvent first, then the
metal ion source added and then the polyanion source can be added
in an alternative embodiment.
[0037] In the preferred embodiment the polymeric material is added
first since the polymeric material is soluble in the solvent it is
easy to discern when the polymeric material is dissolved. The
polyanion source, preferably a phosphate source, is then added in
the preferred embodiment. The phosphate source is also soluble in
the solvent and therefore it can be readily determined when the
phosphate source is dissolved. The metal ion is added last in that
the metal ion does not dissolve in the solvent and may color the
solution, as in the case of V.sub.2O.sub.3 the solution turns
black.
[0038] In a preferred embodiment of the present invention an amount
of polymeric material is dissolved in water to form a first
solution. The alkali metal polyanion, lithium hydrogen phosphate
(LHP) is added to the first solution while stirring to form a first
slurry. A source of metal ion is added to the first slurry while
stirring to produce a second slurry. The second slurry is then
dried for 24 hours at a temperature greater than the boiling point
of the solvent. The resulting dried powder is then pelletized and
fired in a tube furnace.
[0039] Without being limited hereby, it is believed that the
polymeric material acts as a phase separation inhibitor during
drying, heating and firing. In addition when used as such the
polymeric material acts as an electron conductivity promoter in the
final products. The polymeric material additionally serves as a mix
aid during the process by holding the reactants tightly together
which produces a highly condensed products that have a higher tap
density than materials made by the method of the '033 patent.
[0040] By way of example, in the preparation of lithium vanadium
phosphate, using the method of the present invention, (outlined
above and more fully described in detail in the Examples) the
preferred polymeric material, either polyethylene glycol (PEG) or
polyethylene oxide (PEO) is dissolved in water with stirring. PEG
and PEO are soluble in the solvent, water. The preferred polyanion
source, lithium hydrogen phosphate (LHP) is then added to the
solvent, water, containing the dissolved polymeric material while
stirring to form a first slurry. The polyanion source LHP is also
soluble in the solvent, water. Then the metal ion source
(V.sub.2O.sub.3) is added to the first slurry with stirring to form
a second slurry. During drying, heating and firing, the polymeric
material serves as a "holder" by holding the LHP on the surface of
the V.sub.2O.sub.3. In doing this, the reaction between the LHP and
V.sub.2O.sub.3 can be more efficient and go further to completion
without phase separation occurring among the reactants. During the
processing the polymeric material melts and changes substance form
from liquid, to gel, to solid and forms a conductive network
throughout the electroactive materials produced.
[0041] In an alternate embodiment, a source of carbon can be added
to the reaction mixture. The carbon can be added to the first or
second slurry or can be added to the essentially dried mixture
before heating. If the carbon is added to the essentially dried
mixture the mixture and the carbon are ball milled or mixed by
another means to produce a uniform mixture prior to heating The
carbon used can be an elemental carbon, preferably in particulate
form such as graphites, amorphous carbon, carbon blacks and the
like. In another aspect the carbon can be provided by an organic
precursor material, or by a mixture of elemental carbon and an
organic precursor material. By organic precursor material is meant
a material made up of carbon and hydrogen, containing no
significant amounts of other elements and that is capable of
forming a decomposition product that contains carbon. Examples of
such organic precursor materials include, but are not limited to,
coke, organic hydrocarbons, alcohols, esters, ketones, aldhydes,
carboxylic acids, sulfonates, ethers, sugars, other carbohydrates,
polymers and the like. The carbon or organic precursor material is
added in an amount from about 0.1 weight percent to about 30 weight
percent, preferably from about 1 weight percent to about 12 weight
percent and more preferably from about 6 weight percent to about 12
weight percent.
[0042] The carbon remaining in the reaction product functions as a
conductive constituent in the ultimate electrode or cathode
formulation. This is an advantage since such remaining carbon is
very intimately mixed with the reaction product material.
[0043] In a preferred embodiment of the invention the solvent used
is water and in particular deionized water. However it would be
apparent to one skilled in the art that any organic solvent would
be useful herein when the polymeric material is soluble therein and
as long as the solvent does not interact with the polymeric
material or the polyanion source to adversely affect the desired
product of the final product. Such solvents are preferably volatile
and include, but are not limited to, deionized water, water,
dimethylsulfoxide (DMSO), N-methylpyrrolidinone (NMP), propylene
carbonate (PC), ethylene carbonate (EC), dimethylformamide (DMF),
dimethyl ether (DME), tetrahydrofuran (THF), butyrolactone (BL) and
the like. Preferably the solvent should have a boiling point in the
range from about 25.degree. C. to about 300.degree. C.
[0044] The polymeric material as used in the present process acts
as a "conductive network former". The process of the present
invention produces an admixture of the polymeric material with the
metal polyanion or mixed metal polyanion, followed by heating
wherein the polymeric material upon heating forms an electron
conductive network within the final metal polyanion product or
within the final mixed metal polyanion product.
[0045] The polymeric material is an organic substance preferably
composed of carbon, oxygen and hydrogen, with amounts of other
elements in quantity low enough to avoid interference with the
synthesis of the metal polyanion or mixed metal polyanion and to
avoid interference with the operation of the metal polyanion or
mixed metal polyanion when used in a cathode. The presence and
effectiveness of the conductive network can be detected using
powder resistivity measurements. Such measurements, in general,
have indicated a high resistivity for lithium metal phosphates
produced by the method of the '033 patent and a more desirable low
resistivity for the lithium metal phosphates produced by the
process of the present invention.
[0046] Powder resistivity measures the resistivity of composite
materials in powder form. In the case of composite materials that
are comprised primarily of insulating powders with small amounts of
conductive materials, the resistivity of the composite will be
governed by the amount of conductive material present and its
pattern of distribution throughout the composite. In theory,
without being limited thereby, it is believed that the optimal
distribution of conductive material, for reducing the resistivity
of a composite material is a network, wherein the conductive
material forms continuous current paths or series of current paths
throughout the composite material. In theory, without being limited
thereby, the polymeric material as used in the process of the
present invention, upon heating produces such current paths to form
a conductive network throughout the metal polyanions and mixed
metal polyanions. With such a conductive network current can flow
throughout the composite materials and resistivity of the composite
is minimized.
[0047] The polymer is chosen so that it is soluble in the volatile
solvent to be used in the process of the present invention. The
polymer can be in liquid or solid form. If the polymer is in solid
form it cannot have a melting point greater than the temperature at
which the second heating step occurs. It follows that a polymer
with too high of a melting point is generally less soluble than
polymers with lower melting points and therefore may not be
uniformly distributed throughout the reaction product. The
polymeric material is added in an amount from about 1 weight
percent to about 55 weight percent, and preferably in an amount
from about 3 weight percent to about 12 weight percent and more
preferably in an amount from about 6 weight percent to about 12
weight percent.
[0048] In a preferred embodiment of the invention the polymeric
material is poly(oxyalkylene) ether and more preferably is
polyethylene oxide (PEO) or polyethylene glycol (PEG) or mixtures
thereof. However, it would be apparent to one with skill in the art
that other polymeric materials would be useful in the methods of
the present invention. Polymers containing predominantly or
entirely carbon and hydrogen in the polymer chain are preferred.
For example the polymeric material may include without limitation,
carboxy methyl cellulose (CMC), ethyl hydroxylethyl cellulose
(EHEC), 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 of
those described above.
[0049] Preferably the polymeric material is compatible with the
operation of the metal polyanion or mixed metal polyanion when used
as a cathode active material in a cell. It is therefore preferred
that residual amounts of the polymeric material will not interfere
with the operation of the cell. Preferred polymers include
polyethylene oxide, polyethylene, polyethylene glycol,
carboxymethyl cellulose, ethyl hydroxylethyl cellulose and
polypropylene. Polyethylene oxide is one preferred polymerin view
of its known use as an electrolyte in lithium polymer
batteries.
[0050] Preferably the polymeric material is added during synthesis
in order to reduce the number of steps involved in preparing the
electroactive materials. However, the polymeric material may be
added to the metal polyanion or mixed metal polyanion during or
after synthesis of the metal polyanion or mixed metal polyanion. In
a preferred embodiment the polymeric material should be compatible
with the starting materials used to form the metal polyanion or
mixed metal polyanion. In a particularly preferred embodiment the
polymeric material should be miscible with molten lithium
dihydrogen phosphate. In this manner polyethylene oxide is again a
preferred polymer because of its hydrophilic nature.
[0051] Polyanion sources include, but are not limited to,
polyanion-containing compounds wherein the polyanion containing
compound is selected from the group consisting of a
PO.sub.4-containing compound, a SiO.sub.4 containing compound, a
GeO.sub.4-containing compound, a VO.sub.4-containing compound, an
AsO.sub.4-containing compound, a SbO.sub.4-containing compound, and
a SO.sub.4-containing compound. Preferably the polyanion-containing
compound is a PO.sub.4-containing compound. More preferably the
PO.sub.4-containing compound is selected from the group consisting
of diammonium hydrogen phosphate, ammonium dihydrogen phosphate,
lithium dihydrogen phosphate and mixtures thereof. Representative
alkali metal polyanions include, but are not limited to
LiH.sub.2PO.sub.4 and NaH.sub.2PO.sub.4, and the like. Sources
containing both an alkali metal and a polyanion can serve as both
an alkali metal source and a polyanion source.
[0052] Sources of metal ions include compounds containing a metal
ion of a metal selected from the group consisting of Ti, V, Cr, Mn,
Fe, Co, Ni, Cu, Mo, Si, Sn, Pb, Be, Mg, Ca, Sr, Ba, Zn, Cd, Ge, Sc,
Y, B, Al, Ga, In and mixtures thereof. Examples of such metal ion
sources include, but are not limited to Fe.sub.2O.sub.3,
CO.sub.3O.sub.4, Mn.sub.2O.sub.3, Fe.sub.3O.sub.4, FeO, CoO,
MnO.sub.2, MnO, magnesium hydroxide, magnesium carbonate, magnesium
acetate, magnesium oxide, calcium hydroxide, calcium carbonate,
calcium acetate, calcium oxide, calcium phosphate, calcium carbide,
calcium citrate tetrahydrate, Ca(NO.sub.3).sub.2, zinc hydroxide,
zinc carbonate, zinc acetate, zinc oxide, zinc phosphate, zinc
powder, zinc citrate dehydrate, nickel carbonate, nickel acetate,
nickel oxides, nickel hydroxide, nickel oxalate, cobalt acetate,
cobalt oxide, Co(OH).sub.2, cobalt oxalate, copper (II) acetate,
copper (II) carbonate, copper (II) oxide, aluminum hydroxide,
aluminum carbonate, aluminum acetate, aluminum oxide, boron
hydroxide, boron oxide, B.sub.2O.sub.3, boron phosphate, chromium
acetate, chromium oxide, Cr.sub.2O.sub.3, chromium acetylacetonate,
Nb.sub.2O.sub.5, Nb(OC.sub.6H.sub.5).sub.5 and the like. In
addition some of the starting materials can serve as both the
source of the polyanion and the source of the metal ion. By way of
example, Fe.sub.3(PO.sub.4).sub.2 8H.sub.2O can serve as a source
of the metal ion (Fe) and a source of the polyanion
(phosphate).
[0053] Preferred metal ion sources wherein the metal polyanion
formed contains one metal ion, are compounds containing an ion of a
metal selected from the group consisting of Ti, V, Cr, Mn, Fe, Co,
Ni, Cu, Mo, Si, Sn and Pb. In an alternate embodiment wherein the
mixed metal polyanion formed contains more than one metal ion, the
preferred second metal ion source is a compound containing an ion
of a metal selected from the group described above or mixtures
thereof; or compounds containing an ion of a metal selected from
the group consisting of Be, Mg, Ca, Sr, Ba, Zn, Cd, Ge, Sc, Y, B,
Al, Ga, In and mixtures thereof.
[0054] The starting materials are mixed in a stoichiometric
proportion which provides the desired nominal general formula:
A.sub.aMI.sub.bMII.sub.c(XY.sub.4).sub.dZ.sub.e
[0055] wherein: [0056] (i) A comprises at least one alkali metal
selected from the group consisting of Li, Na, K, and mixtures
thereof and 0<a.ltoreq.6; [0057] (ii) MI comprises a metal ion
of a metal selected from the group consisting of Ti, V, Cr, Mn, Fe,
Co, Ni, Cu, Mo, Si, Sn, Pb and mixtures thereof and
0<b.ltoreq.4; [0058] (iii) MII comprises a metal ion of a metal
selected from the group consisting of Be, Mg, Ca, Sr, Ba, Zn, Cd,
Ge, Sc, Y, B, Al, Ga and mixtures thereof and 0.ltoreq.c.ltoreq.4;
[0059] (iv) XY.sub.4 is selected from the group consisting of
X'[O.sub.4-xY'.sub.x], X[O.sub.4-yY'.sub.2y], X''S.sub.4,
[X.sub.z''',X'.sub.1-z]O.sub.4 and mixtures thereof wherein: [0060]
(a) X' and X''' are each independently selected from the group
consisting of P, As, Sb, Si, Ge, S and mixtures thereof; [0061] (b)
X'' is selected from the group consisting of P, As, Sb, Si, Ge, V
and mixtures thereof; [0062] (c) Y' is selected from the group
consisting of a halogen, and mixtures thereof; and [0063] (d)
0=x=3, 0<y<2, and 0<z<1, and [0064] (i) Z is selected
from the group consisting of OH, a halogen and mixtures thereof,
and 0<d=6; [0065] wherein A, M, X, Y, Z, a, b, x, y, z, c and d
are selected so as to maintain electroneutrality of the material.
In a preferred embodiment the amount of polyanion source is added
in excess of the stoichiometric proportion. A preferred excess is
in an amount from about 0.1% to about 4% and more preferably is an
excess in amount from about 0.5% to about 2%.
[0066] In preferred embodiments this invention relates to a method
of preparing compounds of the nominal general formula:
LiFePO.sub.4, Li.sub.3V.sub.2(PO.sub.4).sub.3, Li.sub.3.03
V.sub.2(PO.sub.4).sub.3.09 and LiFe.sub.1-xMg.sub.xPO.sub.4.
[0067] The term milling as used herein often times specifically
refers to ball milling. However, it is understood by those skilled
in the art, that the term as used herein and in the claims can
encompass processes similar to ball milling which would be
recognized by those with skill in the art. For instance, the
starting materials can be blended together, put in a commercially
available muller and then the materials can be mulled.
Alternatively, the starting materials can be mixed by high shear
and/or using a pebble to mix the materials in a slurry form.
[0068] In a preferred process the polymer is added to the solvent
and stirred until the polymer is dissolved. This stirring of the
solution until the polymer dissolves can be completed in about 1
minute to about 10 hours and preferably from about 2 minutes to
about 5 hours. The polyanion source is then added with stirring to
form a slurry A. The slurry is again stirred from about 1 minute to
about 10 hours and preferably from about 2 minutes to about 5
hours. In a preferred embodiment the polyanion source is lithium
hydrogen phosphate which is soluble in the solvent. The metal ion
source is then added with stirring from about 1 minute to about 10
hours and more preferably from about 2 minutes to about 5 hours.
One skilled in the art will recognize that stirring times can vary
depending on factors such as temperature and size of the reaction
vessel and amounts and choice of starting materials. The stirring
times can be determined by one skilled in the art based on the
guidelines given herein and choice of reaction conditions and the
sequence that the starting materials are added to the slurry.
[0069] The slurry, containing the solvent, the polymer, the
polyanion and the metal, are heated at a temperature greater than
the boiling point of the solvent. Typically the slurry is heated at
a temperature of about 80.degree. C. to about 200.degree. C., more
preferably at about 100.degree. to about 150.degree. C., and most
preferably at about 110.degree. C. The heating is carried out over
a period of time to evaporate essentially all of the solvent and to
produce an essentially dried mixture. Typically the slurry is
heated over a time period of from about 2 hours to about 48 hours,
more preferably from about 6 hours to about 24 hours, and
preferably for about 12 hours. After such heating step an
essentially dried mixture is formed.
[0070] The dried mixture is then milled, mulled or milled and
mulled for about 4 hours to about 24 hours, preferably from about
12 to about 24 hours and more preferably for about 12 hours. The
amount of time required for milling is dependent on the intensity
of the milling. For example, in small testing equipment the milling
takes a longer period of time then is needed with industrial
equipment.
[0071] The milled mixture is then heated in an inert atmosphere,
such as nitrogen or argon. The mixture is heated at a temperature
from about 650.degree. C. to about 1000.degree. C., preferably from
about 700.degree. C. to about 900.degree. C. and more preferably at
about 900.degree. C. The heating period is from about 1 hour to
about 24 hours and preferably from about 4 to about 16 hours and
more preferably about 8 hours. The heating rate is typically about
2.degree. C. per minute to about 5.degree. C. per minute and
preferably about 2.degree. C. per minute.
[0072] Optionally the mixture can be heated in two steps. The
mixture can first be heated at a temperature from about 250.degree.
C. to about 600.degree. C. and more preferably from about
300.degree. C. to about 500.degree. C. and preferably at about
400.degree. C. The initial heating period is from about 1 hour to
about 24 hours and preferably from about 2 to about 12 hours and
more preferably about 2 hours. The heating rate is typically about
2.degree. C. per minute to about 5.degree. C. per minute and
preferably about 2.degree. C. per minute.
[0073] Although the initial step is optional it is believed,
without being limited thereto, that such initial heating step may
be beneficial in producing a product with electrochemical
performance that is better than a product without such an initial
heating step. It is believed that this is because the initial
heating step removes essentially all of the moisture so that in the
second heating step the starting materials can react more
completely. This initial heating step may especially be more
beneficial in larger furnaces where any remaining solvent or water
may go to the bottom of the furnace.
[0074] Preferably the metal polyanions and mixed metal polyanions
produced by the above steps are cooled slowly at a fixed rate.
Preferably the polyanions are cooled at a rate of about 2.degree.
C. per minute to about 3.degree. C. per minute. More preferably the
materials are cooled at a rate of about 2.degree. C. per
minute.
[0075] In another embodiment of the invention it has now
surprisingly been found these classes of compounds, and compounds
similar to those disclosed in U.S. Pat. No. 6,528,033 B1 can be
prepared in a beneficial manner to produce materials with high
electron conductivity without the use of a solvent. The method
employs a polymeric material which acts a phase separation
inhibitor in the dry mix method. The polymeric material also acts
to form a conductive network throughout the materials produced by
the process of the present invention due to the melting and or
decomposition of the polymer during the process and distribution of
the decomposed polymer throughout the final product. It has been
found that materials so produced exhibit high electronic
conductivity when used as the active materials in electrodes,
preferably as cathodes.
[0076] In one embodiment of the invention a metal polyanion or
mixed metal polyanion is produced by a dry mix method. The process
comprises forming a mixture comprising a polymeric material, a
polyanion source and a source of at least one metal ion and heating
the mixture so formed, drying and milling the material so produced
and heating the resulting product to produce an electroactive metal
polyanion or an electroactive mixed metal polyanion. The sources
and reactions conditions other than the solvents and those that
follow are the same as described for the solvent process described
above.
[0077] The milled mixture is heated in an inert atmosphere, such as
nitrogen or argon. The mixture is heated at a temperature from
about 650.degree. C. to about 1000.degree. C., preferably from
about 700.degree. C. to about 900.degree. C. and more preferably at
about 900.degree. C. The heating period is from about 1 hour to
about 24 hours and preferably from about 4 to about 16 hours and
more preferably about 8 hours. The heating rate is typically about
2.degree. C. per minute to about 5.degree. C. per minute and
preferably about 2.degree. C. per minute.
[0078] Optionally the mixture can be heated in two steps after the
drying and milling. The mixture can first be heated at a
temperature from about 250.degree. C. to about 600.degree. C. and
more preferably from about 300.degree. C. to about 500.degree. C.
and preferably at about 400.degree. C. The initial heating period
is from about 1 hour to about 24 hours and preferably from about 2
to about 12 hours and more preferably about 2 hours. The heating
rate is typically about 2.degree. C. per minute to about 5.degree.
C. per minute and preferably about 2.degree. C. per minute.
[0079] Although the initial step is optional it is believed,
without being limited thereto, that such initial heating step may
be beneficial in producing a product with electrochemical
performance that is better than a product without such an initial
heating step. It is believed that this is because the initial
heating step removes essentially all of the moisture so that in the
second heating step the starting materials can react more
completely.
[0080] By way of further example, the first step of the process
comprises mixing a polymeric material, such as polyethylene oxide
(PEO) having a melting point of approximately 150.degree. C. (PEO
with a MW of 20,000), a polyanion source, such as
LiH.sub.2PO.sub.4, and a metal ion source such as V.sub.2O.sub.3 to
form a mixture. The mixture is then blended using a high speed
blender to produce a fine mixture. The fine mixture is then heated.
In a preferred embodiment wherein the polymeric material is PEO or
PEG the mixture is heated to 110.degree. C. The resulting material
is dried and ball milled. The resulting material is then heated
under argon gas at 400.degree. C. for two hours and then further
heated at 900.degree. C. for 8 hours than cooled to room
temperature. The powder is then milled and sieved to the desired
particle size to produce a metal phosphate or mixed metal phosphate
material with high electronic conductivity.
[0081] Without being limited hereby, it is believed that the
polymeric material acts as a phase separation inhibitor during
drying, heating and firing. In addition when used as such the
polymeric material acts as an electron conductivity promoter in the
final products in that upon melting or decomposing the polymeric
material forms a conductive network throughout the product. The
polymeric material additionally serves as a mix aid during the
process by holding the reactants tightly together resulting in
highly condensed products that have a higher tap density than
materials made by the previous method of the '033 patent.
[0082] By way of example, in the preparation of lithium vanadium
phosphate using the method of the present invention, (outlined
above and more fully described in detail in the Examples) the
preferred polymeric material, polyethylene oxide (PEO) or
polyethylene glycol (PEG) is added to a mixture of a polyanion
source, lithium hydrogen phosphate (LHP) and a metal ion source
(V.sub.2O.sub.3). The resulting mixture is then blended using a
high speed blender to produce a fine mixture. The fine mixture is
then heated. The resulting mixture is then ball milled. The
material is then heated under argon at 900.degree. C. to form the
desired product. The product can then be hammer milled and sieved
to the desired particle size.
[0083] It is believed without being limited thereby that during
drying, heating and firing, the polymeric material serves as a
"holder" by holding the LHP on the surface of the
V.sub.2O.sub.3--In doing this, the reaction between the LHP and
V.sub.2O.sub.3 can be more efficient, go further to completion
without phase separation occurring among the reactants. During the
processing the polymeric material melts or decomposes and changes
substance form from liquid, to gel, to solid and forms a conductive
network throughout the materials produced.
[0084] The term blending as used is a conventional procedure known
to those with skill in the art using a high speed blender. However
it is understood by those skilled in the art that the term as used
herein and in the claims can encompass processes similar to
blending which would be recognized by those with skill in the art,
such as a V-blender and the like. The materials are blended for a
period of time from about 4 minutes to about 16 hours and more
preferably from about 30 minutes to about 2 hours.
[0085] The dried mixture is then milled, mulled or milled and
mulled for about 8 hours to about 24 hours, preferably from about
12 to about 24 hours and more preferably for about 12 hours. The
amount of time required for milling is dependent on the intensity
of the milling. For example, in small testing equipment the milling
takes a longer period of time then is needed with industrial
equipment.
[0086] The milled mixture is then heated in an inert atmosphere,
such as nitrogen or argon. The mixture is heated at a temperature
from about 650.degree. C. to about 1000.degree. C., preferably from
about 700.degree. C. to about 900.degree. C. and more preferably at
about 900.degree. C.
[0087] The heating period is from about 4 hours to about 24 hours
and preferably from about 4 to about 24 hours and more preferably
about 8 hours. The heating rate is typically about 2.degree. C. per
minute to about 5.degree. C. per minute and preferably about
2.degree. C. per minute.
[0088] Preferably the metal polyanions and mixed metal polyanions
produced by the above steps are cooled slowly at a fixed rate.
Preferably the polyanions are cooled at a rate of about 2.degree.
C. per minute to about 3.degree. C. per minute. More preferably the
materials are cooled at a rate of about 2.degree. C. per
minute.
[0089] In preferred embodiments this invention relates to a method
of preparing compounds of the nominal general formula:
LiFePO.sub.4, Li.sub.3V.sub.2(PO.sub.4).sub.3,
Li.sub.3.03V.sub.2(PO.sub.4).sub.3.09 and
LiFe.sub.1-xMg.sub.xPO.sub.4.
[0090] The lithium metal phosphates and lithium mixed metal
phosphate of the present invention are usable as electrode active
materials, for lithium ion (Li.sup.+) removal and insertion. These
electrodes are combined with a suitable counter electrode to form a
cell using conventional technology known to those with skill in the
art. Upon extraction of the lithium ions from the lithium metal
phosphates or lithium mixed metal phosphates, significant capacity
is achieved.
[0091] The electroactive metal polyanion or the electroactive mixed
metal polyanion produced by the processes of the present invention
can further be milled and sieved to the desired particle size. The
particle size is preferably from about 2 .mu.m to about 10 .mu.m
and more preferably from about 2 .mu.m to about 5 .mu.m.
[0092] The following is a list of some of the definitions of
various terms used herein:
[0093] 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, cathode, and an
electrolyte.
[0094] 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.
[0095] As used herein the tern "nominal formula" or "nominal
general formula" refers 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.
[0096] 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 does not imply that other embodiments are not
useful and is not intended to exclude other embodiments from the
scope of the invention.
[0097] The following is a list of some of the abbreviations and the
corresponding meanings as used interchangeably herein:
[0098] C/5 rate=5 hour rate
[0099] mAh/g=milliamp hours per gram
[0100] XRD=x-ray diffraction
[0101] The following Examples are intended to be merely
illustrative of the present invention, and not limiting thereof in
either scope or spirit. Those with skill in the art will readily
understand that known variations of the conditions and processes
described in the Examples can be used to synthesize the compounds
of the present invention.
[0102] Unless otherwise indicated all starting materials and
equipment employed were commercially available.
EXAMPLE 1
Preparation of LVP by Wet Mixing
[0103] Polyethylene glycol (10 g, MW 2,000) and PEO (2 g) were
added to H.sub.2O (50 g) while stirring to produce a solution A.
LiH.sub.2PO.sub.4 (50 g) was added to solution A while stirring to
produce a slurry B. V.sub.2O.sub.3 (23.79 g) was added to slurry B
while stirring to produce slurry C. Slurry C was placed in a glass
container and the mixture was heated to 110.degree. C. for 12 hours
to form a dried mixture.
[0104] The resulting dried mixture was then ball-milled for 12
hours. The resulting material was then heated to 400.degree. C. at
a rate of 3.degree. C./minute and then heated at 400.degree. C. for
two hours under argon (Ar) gas. The material was further heated to
900.degree. C. at a rate of 5.degree. C./minute under argon gas and
then heated at 900.degree. C. for 8 hours. The material was then
cooled to room temperature at a rate of 5.degree. C./minute. The
material was then hammer milled and sieved to the desired particle
size between about 2 and about 30 .mu.m for electrochemical testing
and characterization.
[0105] FIG. 1 shows the XRD of the material so produced.
[0106] FIG. 2 shows the voltage vs. time profile of the polymeric
LVP so produced.
[0107] FIG. 3 shows the cycling behavior and voltage profile of the
polymeric LVP at C/2.
Testing Data:
Tap density; 1.758 g/ml
Residual carbon: .about.0.5%
Resistivity (ohm.sup.-cm): 1.78E+03
EXAMPLE 2
Preparation of LVP by Wet Mixing (5 kg Batch)
[0108] Polyethylene glycol (400 g, MW 1,000) and PEO (20 g) was
added to H.sub.2O (3600 g) while stirring to produce a solution A.
LiH.sub.2PO.sub.4 (4000 g) was added to solution A while stirring
to produce a slurry B. V.sub.2O.sub.3 (1903.2 g) was added to
slurry B while stirring to produce slurry C. Slurry C was placed in
a glass container and the mixture was heated to 110.degree. C. and
then heated at 110.degree. for 12 hours to form a dried
mixture.
[0109] The resulting dried mixture was then mulled for 12 hours and
then ball milled for 12 hours. The resulting material was then
heated to 400.degree. C. at a rate of 3.degree. C./minute and then
heated at 400.degree. C. for two hours under argon (Ar) gas. The
material was further heated to 900.degree. C. at a rate of
5.degree. C./minute under argon gas and then heated at 900.degree.
C. for 8 hours. The material was then cooled to room temperature at
a rate of 5.degree. C./minute. The material was then hammer milled
and sieved to the desired particle size for electrochemical testing
and characterization.
[0110] FIG. 4 shows the XRD of the material so produced.
[0111] FIG. 5 shows the voltage vs. time profile of the polymeric
LVP so produced.
[0112] FIG. 6 shows the cycling behavior and voltage profile of the
polymeric LVP at C/2.
Testing Data:
Tap density: 1.156 g/ml
Residual carbon: .about.0.5%
Resistivity (ohm.sup.-cm): 3.4E+03
EXAMPLE 3
Preparation of LVP by Wet Mixing (Super-P Carbon)
[0113] PEO (1.8 g, MW 20,000) was added to H.sub.2O (100 g) while
stirring to produce a solution A. LiH.sub.2PO.sub.4 (100 g) was
added to solution A while stirring to produce a slurry B.
V.sub.2O.sub.3 (47.58 g) was added to slurry B while stirring to
produce slurry C. Super-P carbon black (4.8 g) was then added to
slurry C while stirring to produce slurry D. Slurry D was placed in
a glass container and the mixture was heated to 110.degree. C. and
then heated at 110.degree. C. for 12 hours to form a dried
mixture.
[0114] The resulting dried mixture was then mulled for 12 hours and
then ball milled for 12 hours. The resulting material was then
heated to 400.degree. C. at a rate of 3.degree. C./minute and then
heated at 400.degree. C. for two hours under argon (Ar) gas. The
material was further heated to 900.degree. C. at a rate of
5.degree. C./minute under argon gas and then heated at 900.degree.
C. for 8 hours. The material was then cooled to room temperature at
a rate of 5.degree. C./minute. The material was then hammer milled
and sieved to the desired particle size for electrochemical testing
and characterization.
[0115] FIG. 7 shows the XRD of the material so produced.
[0116] FIG. 8 shows the cycling behavior of the polymeric LVP at a
current rate of C/2.
Testing Data:
Tap density: 1.40 g/ml
Residual carbon: .about.4.0%
Resistivity (ohm.sup.-cm): 8.57E+00
EXAMPLE 4
Preparation of LiFe.sub.0.95Mg.sub.0.05PO.sub.4 by Wet Mixing
(Super-P Carbon)
[0117] PEO (10 g, MW 20,000) was added to H.sub.2O (200 g) while
stirring to produce a solution A. LiH.sub.2PO.sub.4 (104.6 g) and
Mg(OH).sub.2 (2.9 g) were added to solution A while stirring to
produce a slurry B. Fe.sub.2O.sub.3 (80 g) was added to slurry B
while stirring to produce slurry C. Super-P carbon black (2.0 g)
was then added to slurry C while stirring to produce slurry D.
Slurry D was the blended by high speed blender and then placed in a
glass container. The mixture was heated to 110.degree. C. and then
heated at 110.degree. C. for 12 hours to form a dried mixture.
[0118] The resulting dried mixture was then mulled for 12 hours and
then ball milled for 12 hours. The resulting material was then
heated to 30.degree. C. at a rate of 1.degree. C./minute and then
heated at 30.degree. C. for fifteen minutes under argon (Ar) gas.
The material was further heated to 85.degree. C. at a rate of
2.degree. C./minute under argon gas and then heated at 85.degree.
C. for 20 minutes. The material was further heated to 750.degree.
C. at a rate of 2.degree. C./minute under argon gas and then heated
at 750.degree. C. for 4 hours. The material was then cooled to room
temperature (21.degree. C.) at a rate of 2.degree. C./minute. The
material was then hammer milled and sieved to the desired particle
size for electrochemical testing and characterization.
[0119] FIG. 9 shows the XRD of the material so produced.
Testing Data:
Tap density: 1.8 g/ml
Residual carbon: .about.2.5%
Resistivity (ohm.sup.-cm): 2.3E+00
EXAMPLE 5
Preparation of LVP (Dry Mixing)
[0120] PEO (50 g, MW 20,000) was added to a mixture of
LiH.sub.2PO.sub.4 (250 g) and V.sub.2O.sub.3 (118.1 g). The
resulting mixture was then blended using a high speed blender to
produce a fine mixture. The mixture was then placed into a glass
container and heated to 110.degree. C. The mixture was heated at
110.degree. C. for 12 hours. The resulting mixture was then ball
milled for 4 hours. The resulting material was then heated to
400.degree. C. at a rate of 3.degree. C./minute and then heated at
400.degree. C. for 2 hours under argon gas. The material was then
heated to 900.degree. C. at a rate of 5.degree. C./minute under
argon gas then heated at 900.degree. C. for 8 hours. The material
was then cooled to room temperature at a rate of 5.degree.
C./minute. The material was then hammer milled and sieved to the
desired particle size for further electrochemical testing.
[0121] FIG. 10 shows the XRD of the material so produced
[0122] FIG. 11 shows the cycling behavior of the material at a
current rate of C2.
EXAMPLE 6
Preparation of LVP (Dry Mixing-Super-P)
[0123] PEO (50 g, MW 20,000) was added to a mixture of
LiH.sub.2PO.sub.4 (250 g), V.sub.2O.sub.3 (118.1 g) and Super-P
carbon black (3.6 g). The resulting mixture was then blended using
a high speed blender to produce a fine mixture. The mixture was
then placed into a glass container and heated to 110.degree. C. The
mixture was heated at 110.degree. C. for 12 hours. The resulting
mixture was then ball milled for 4 hours. The resulting material
was then heated to 400.degree. C. at a rate of 3.degree. C./minute
and then heated at 400.degree. C. for 2 hours under argon gas. The
material was then heated to 900.degree. C. at a rate of 5.degree.
C./minute under argon gas then heated at 900.degree. C. for 8
hours. The material was then cooled to room temperature at a rate
of 5.degree. C./minute. The material was then hammer milled and
sieved to the desired particle size for further electrochemical
testing.
[0124] FIG. 12 shows the XRD of the material so produced
[0125] FIG. 13 shows the cycling behavior of the material at a
current rate of C/2.
EXAMPLE 7
Preparation of LVP (Wet Mixing-EHEC)
[0126] Ethyl hydroxylethyl cellulose (EHEC) (40 g, MW 1,000) was
added to H.sub.2O (360 g) while stirring to produce a solution A.
LiH.sub.2PO.sub.4 (400 g) was added to solution A while stirring to
produce a slurry B. V.sub.2O.sub.3 (190.3 g) was added to slurry B
while stirring to produce slurry C. Slurry C was placed in a glass
container and the mixture was heated to 110.degree. C. and then
heated at 110.degree. C. for 12 hours to form a dried mixture.
[0127] The resulting dried mixture was then mulled for 12 hours and
then ball milled for 12 hours. The resulting material was then
heated to 400.degree. C. at a rate of 3.degree. C./minute and then
heated at 400.degree. C. for two hours under argon (Ar) gas. The
material was further heated to 900.degree. C. at a rate of
5.degree. C./minute under argon gas and then heated at 900.degree.
C. for 8 hours. The material was then cooled to room temperature at
the rate of 5.degree. C./minute. The material was then hammer
milled and sieved to the desired particle size between 2 and 30
.mu.m for electrochemical testing and characterization.
[0128] FIG. 14 shows the cycling behavior of the material at a
current rate of C/2.
EXAMPLE 8
Preparation of LVP (Wet Mixing Peg)
[0129] Polyethylene glycol (PEG) (100 g, MW 1000) was added to
H.sub.2O (900 g) while stirring to produce a solution A.
LiH.sub.2PO.sub.4 (1000 g) was added to solution A while stirring
to produce a slurry B. V.sub.2O.sub.3 (475.8 g) was added to slurry
B while stirring to produce a slurry C. Slurry C was placed in a
glass container and the mixture was heated to 110.degree. C. for 12
hours to form a dried mixture. (PEG MW 1000 has a melting point of
approximately 30.degree. C. so it is in liquid phase at room
temperature).
[0130] The resulting dried mixture was then ball milled for 12
hours. The resulting material was then heated to 400.degree. C. at
a rate of 3.degree. C./minute and then heated at 400.degree. C. for
2 hours under argon (Ar) gas. The material was then further heated
to 900.degree. C. for 8 hours. The material was then cooled to room
temperature at a rate of 5.degree. C./minute under argon gas. The
material was then cooled to room temperature at a rate of 5.degree.
C./minute. The material was then hammer milled and sieved to the
desired particle size between 2 and 30 .mu.m for electrochemical
testing and characterization.
[0131] FIG. 15 shows the cycling behavior of the material at a
current rate of C/2.
[0132] The compounds produced by the above described methodology
find use as active materials for electrodes in ion batteries and
more preferably in lithium ion batteries. The lithium metal
phosphates and lithium mixed metal phosphates produced by the
present invention are useful as active materials in electrodes of
batteries, and more preferably are useful as active materials in
positive electrodes (cathodes). When used in the positive
electrodes of lithium ion batteries these active materials
reversibly cycle lithium ions with the compatible negative
electrode active material.
[0133] The active material of the compatible counter electrodes is
any material compatible with the lithium metal phosphates or
lithium mixed metal phosphates of the materials of the present
invention. The negative electrode can be made from conventional
anode materials known to those skilled in the art. The negative
electrode can be comprised of a metal oxide, particularly a
transition metal oxide, metal chalcogenide, carbon, graphite, and
mixtures thereof.
[0134] A typical laminated battery in which such material can be
employed includes, but is not limited to batteries disclosed in the
'033 patent. For example a typical bi-cell can comprise a negative
electrode, a positive electrode and an electrolyte/separator
interposed between the counter electrodes. The negative and
positive electrodes each include a current collector. The negative
electrode comprises an intercalation material such as carbon or
graphite or a low voltage lithium insertion compound, dispersed in
a polymeric binder matrix, and includes a current collector,
preferably a copper collector foil, preferably in the form of an
open mesh grid, embedded in one side of the negative electrode. A
separator is positioned on the negative electrode on the side
opposite of the current collector. A positive electrode comprising
a metal phosphate or mixed metal phosphate of the present invention
is positioned on the opposite side of the separator from the
negative electrode. A current collector, preferably an aluminum
foil or grid, is then positioned on the positive electrode opposite
the separator. Another separator is positioned on the side opposite
the other separator and then another negative electrode is
positioned upon that separator. The electrolyte is dispersed into
the cell using conventional methods. In an alternative embodiment
two positive electrodes can be used in place of the two negative
electrodes and then the negative electrode is replaced with a
positive electrode. A protective bagging material can optionally
cover the cell and prevent infiltration of air and moisture. U.S.
Pat. No. 6,528,033 B1, Barker et al. is hereby incorporated by
reference.
[0135] The electrochemically active compounds of the present
invention can also be incorporated into conventional cylindrical
electrochemical cells such as described in U.S. Pat. No. 5,616,436,
U.S. Pat. No. 5,741,472 and U.S. Pat. No. 5,721,071 to Sonobe et
al. Such cylindrical cells consist of a spirally coiled electrode
assembly housed in a cylindrical case. The spirally coiled
electrode assembly comprises a positive electrode separated by a
separator from a negative electrode, wound around a core. The
cathode comprises a cathode film laminated on both sides of a thick
current collector comprising a foil or wire net of a metal.
[0136] An alternative cylindrical cell as described in U.S. Pat.
No. 5,882,821 to Miyasaka can also employ the electrochemically
active materials produced by the method of the present invention.
Miyasaka discloses a conventional cylindrical electrochemical cell
consisting of a positive electrode sheet and a negative electrode
sheet combined via a separator, wherein the combination is wound
together in spiral fashion. The cathode comprises a cathode film
laminated on one or both sides of a current collector.
[0137] The active materials produced by the method of the present
invention can also be used in an electrochemical cell such as
described in U.S. Pat. No. 5,670,273 to Velasquez et al. The
electrochemical cell described therein consists of a cathode
comprising an active material, an intercalation based carbon anode,
and an electrolyte there between. The cathode comprises a cathode
film laminated on both sides of a current collector.
[0138] While this invention has been described in terms of certain
embodiments thereof, it is not intended that it be limited to the
above description. The description of the invention is merely
exemplary in nature and, thus, variations that do not depart from
the gist of the invention are intended to be within the scope of
the invention. Such variations are not to be regarded as a
departure from the spirit and scope of the invention.
* * * * *