Note: Descriptions are shown in the official language in which they were submitted.
.
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SYNTHESIS OF LITHIATED TRANSITION METAL OXIDES
Field of the Invention
The invention relates to a process for the
synthesis of lithiated transition metal oY~ ~oe,, from
lithium compounds and one or more transition metal
oxides, or ~G--I~ounds which doc~mpose to transition
metal oxides, or react directly with the lithium
unds, under the reaction conditions. The produced
lithiated transition metal oxides or lithiated mixed
transition metal oxides are suitable for use as a
cathodic material in lithium ion battery
Background of the Invention
Lithiated transition metal oxide powders, such
as the most . -.~cially used lithium cobalt ~oY~o~
LiCoO2, are utilized as cathode materials for the
positive electrode in rechargeable lithium ion
batteries. Lower cost materials, such as lithium nickel
dioxide and lithium manganese dioxide, would be
preferred, but have proven part~ ~ly laborious to
make, because ut~l~ 7i ng prior art processes for their
preparation involves multiple grinding steps and
calcination stages.
Specific ~h? 1c~l, morphological and physical
characteristics are required to sustain the desired
electrical properties of the lithiated transition metal
oxide powder over the many hundreds of sequential charge
and ~ech~ge cycles ~ o~ during service. Current
battery applications for powders ~f ~n~ high purity
(>99%), homogeneity (of the lithiated structure),
controlled particle sizes (usually within the range of 1
to 25 microns) and specific surface areas (usually
within the range O.1 to 5 m2/g).
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Lithium transition metal O~1~D~ are usually
made by variations on a st~n~d route, namely the
solid state reaction of a preblended mixture of lithium
oxide and the transition metal(II) oxide, in a current
of air or O~yy.2ll, at ~e- ~L'~' atures ranging from about
400~ to 900~C. The lithium oxide is generated in-situ
during the calcination, by the decomposition of a
lithium . , ~nd, usually the carbonate or l-yd oxide.
It is also well known to use other lithium _ , ~nds,
DYDmplary of which is the nitrate. The transition
metal(II) oxide is also usually generated in-situ during
the ~rlc~nAtion, by the ~D~ tion of a transition
metal(II) l_- ,~und. For the syn~hDC~-~ of lithium cobalt
~O~1~D, the transition metal(II) ~...~ou..d is usually
cobalt(II) carbonate, although the nitrate and
hydroxide have also been u~ 7D~.
It is known that good ~Yi ng of the powders,
prior to calcination, rccDlerates formation of the
product as does incrDrs~ng the ~Alc~nAtion ~ ~ ature.
However, t ,-~ature also de~. 1nes the structure of
the product. For DYr _1D, in the case of lithium cobalt
synthDc~7~ at ~AlcinAtion ~ , ~atures as low
as 400~C, lithium cobalt oxide having a spinel structure
is formed, which DYhlh~ts ~ -hAt different properties
to the desired, layered, "rock salt" structure pr~ e~
at 900~C.
Typically, in these prior art methods, as
described for ~ D in U.S. patent 4,302,518 to J.B
~oo~Dno~yh et al., the reaction mixture is preblended,
usually by gr~ n~ ng with a mortar and pestle or in a
ball mill, and the powder may be opt~onAlly _ ~ ted,
before being introduced into the furnace. After a
predeter~ine~ cAlc~nAtion time period, the product is
ved from the furnace, ey~nd and may be ~ cted
again before being ~Al~ n~ for one or more addit~onAl
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time periods to ensure complete conversion to lithium
cobaltic dioxide. The final gr~ nAl ng produces the
desired grain sized powder for use in the battery
cathode.
During recent years the ~mph~c~s of research
work has shifted away from the preparation of the
lithium cobalt dioxide powder per se and ~o.~d the
production of lithiated transition metal compounds
requiring less costly, but equally effective, transition
metals.
The patent literature provides many ~ ~l~s
of other novel lithium ion ~y~t - and variations on the
methods for the preparation thereof. In U.S. patent
5,160,712 issued to M.M Th~-k~ay et al., there are
~i~1ne~ lithium transition metal OY~c and methods
for their preparation. The method comprises ~ ng
the reactants, prior to heating the mixture to a
tem.p~rature c~ 400~~, ~nd ~or a peri~d of ti~.e
sufficient to form an essentially layered lithium
transitions metal oxide structure (which includes
certain spinel type structures), wherein at least part
of the heating is conducted under a suitable G~yy~
cont~i n ~ ng atmosphere.
S~ ~ly, U.S. Patent 4,980,080 to A. Lecerf
et al describes a process for the preparation of a
material suitable for use as a cathode in an
electro~hc i~l cell wherein the starting materials are
a mixture of hydrated lithium hydroxide and ~k~l or
cobalt oxide which are heated in air at ~ atures
ranging between 600~ to 800~C. A two-stage reactant
~i ~i ng and reheating operation is ut~l 1 7~ to thereby
accelerate the process.
As a further example, the hydrides of
lithiated nickel dioxide and the secondary cells
prepared therefrom are ~~ lo~e~ in U.S patent 5,180,574
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issued to U. Von Sacken. The ~---~ounds are prepared
using nickel oxides, nickel hydroxide, and mixtures
thereof, which are reacted with about a twenty five
percent ~yc~cc of lithium hydroxide, at about 600~C in
an atmosphere having a partial pressure of water vapour
greater than two torr.
Despite the number and diversity of these
prior art pro~eccD~ neverth~le~s, there has not been
developed a satisfactory method of controlling the
physical characteristics, such as particle size and
surface area, of lithium cobalt dioxide powder and other
lithium transition metal powders. Further, ~~ ~~cially
viable processes, deleteriously, require multiple
calcination steps. It has also been found that the
prior art processes do not scale up essily without
significant ad~ustments to the proce~es.
Summary of the Invention
It is a primary ob~ective of the present
invention to provide a selection of lithium transition
metal oxide powders having specific particle size and
size distribution and ~ olled microstructure for use
in lithium ion battery ay~ ~ .
It i~ a Lu Ll-er ob~ective to provide a single
stage synthetic route for the production of lithiated
transition metal oxide ~o.l~l 3,
In accordance with the present invention,
there is provided a process for the synth~e~s of lithium
transition metal oxide powders having predeter~i n~
particle size and controlled microstructure which
comprises: reacting one or more transition metal
compounds with a salt, oxide or hydroxide of lithium,
said lithium compound being in a molten phase, and
optionally, an additive which is functional to increase
the effective molten phase ~ ~ature range of said
lithium ~--l~ound, in an atmosphere funct~on~l to control
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the thermal ~composition of said lithium ~ , und and
to maintain, or convert and maintain, the transition
~ metal compound in an oxidation state which corresponds
to the oxidation state of the transition metal in the
product, at a temr~rature and for a time effective to
thereby form the desired lithium transition metal oxide.
Suitable lithium _~Lo~ln~s would be selected
from the salts, oY~s or hyd~ of lithium.
The transition metal compounds would be
selected from the O~ C of cobalt, nickel, manganese,
vanadium, iron, titanium or chromium, or mixtures
thereof. Preferably, the transition metal l_ _ u,-ds
would be selected from the oxides of cobalt, n~ ~1 or
manganese or mixtures thereof. Alternatively, suitable
transition metal ~ , unds would be selected from the
hydroxides, carbonates or salts of cobalt, nickel,
manganese, vanadium or chromium or mixtures thereof.
The additives, which may be utilized
optionally, are believed to ~ e formation of the
liquid phase and extend the t- ,-~ature range of the
molten phase of the lithium compound. The most
effective additives have been found to be Al ~1 ~ metal
~ unds, part~ ~ly potassium or sodium hydroxide or
mixtures thereof, which have very wide ranging molten
t ~eratures ext~n~ng from 300 to above 1200~C. The
preferred additive is potassium l-yd ~ide.
The reaction must be undertaken in an
atmosphere which is L~ on~l to either ~V--~l L the
transition metal l_ , ~nd to an oxide and/or to maintain
the transition metal oxide in the correct oxidation
state namely the same oxidation state as the tran~ition
metal in the final product. Thus, the reaction
atmosphere may ~o...~ lse an inert atmosphere, a r~l-c~ng
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atmosphere or an ~Y~17~ng atmosphere ~ep~n~n~ upon the
nature of the reactants.
As will be evident to one Ck~ 1 in the art,
it is possible to produce the lithium transition metal
oxide powders of predetermined particle size and
controlled mic~o~ cture by controll~ n~ reaction time
and temperature during the heating stage. The
temperature ranges would extend from 200~C to 1200~C and
the residence times from lh to 72h. The elevated
t- ,~ature controls the structure and is n~c~s~y for
the reaction to take place, whereas the residence times
determine the resultant particle size and surface area.
The desired structure defines the reaction temperature
and at this temperature the lithium ~ und and/or
additive must be optimized whereby the lithium compound
and molten medium provide the desired envi ~ t for
growing the partlcl~q with the desired mi~o~L-~L~.e.
The reaction m~-han~sm postulated for the
synthesis of lithium transition metal oxides was
extrapolated from the discovery, that in the synth~s
of lithium cobaltic ~ioY~ from cobalt (III) oxide and
an ~Yc~s~ of lithium carbonate, the lithium carbonate is
ret~ n~ in the molten state during the reaction. The
reaction takes place above 720~C and in a static,
neutral or non-oY~d~ 7i n~ atmosphere, with the lithium
carbonate undergoing partial d~c_ ~osition to form
carbon dioxide which is retained in the static
atmosphere. The reaction thus G~ in the molten
state, under optimum thermodynamic conditions. Without
being bound by same, the molten phase is believed to
exist, under the reaction conditions, as a coating on
the solid transition metal oxide part~le~.
The ~ tion of the atmosphere should
also be ad~usted to control the th~ ~ _ s~tion of
the lithium ~ _~und. For ~ - ,le, if lithium carbonate
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is used, sufficient carbon dioxide should be present in
the atmosphere to retard its thermal ~omro~ition at
reaction t~ -~ature.
As a ~ ~cial process, the process of
the invention has several advantages over the methods of
the prior art. It has the advantage that the
preparation of lithium transition metai oY~ can be
~z~ h~-l in a single high t- -~ature heating step,
in contrast to the prior art methods which require
multiple firings under CAl ~-~ n~tion conditions. Since
the reaction occurs in a molten phase, instead of as a
solid state reaction, it has faster kinetics, thereby
producing a more uniform, h~ _el,eous and repro~-~ihle
powder product with controllable particle size and
growth. Therefore, this improved process is more
A ~hle to large scale ~ ~;ial production.
Advantageously, the produced lithium
transition metal oxide powders exhibit low surface area,
a narrow particle size distribution, and high ch~ ~c
purity.
Description of the Drawings
The method of the invention will now be
described with reference to the A- ,-nying drawings,
in which:
Figure 1 is a y~elAl ~ 7~ process flowsheet for the
production of lithiated transition metal ~o~
powders by the process of the present invention;
Figure 2 is a pho~ oy~aph illustrating lithium
cobalt ~oY~ powder prepared by the process of
the present invention;
Figure 3 is a photo~i~oy aph illustrating lithium
n~ ok~l dioxide powder prepared by the process of
the present invention:
Figure 4 is a histogram illustrating size
distribution ranges for lithium cobalt dioxide
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powder prepared from cobaltic oxide by the process
of the present invention;
Figure 5 is a histogram illustrating size
distribution ranges for lithium cobalt dioxide
powder prepared from cobaltous carbonate by the
process of the present invention:
Figure 6 shows the first charge and ~cc~ge of
the ele~L~ h~ ; C~ 1 cell wherein the cathode was
prepared of LiNiO2 powder prepared by the process
of the invention; and
Figure 7 depicts part of the life cycle of the cell
of Figure 6, with voltages between 4.15 and 3.0
volts.
Description of the Preferred Fmb~ -nt
A finely divided lithium ~G...~ound and one or
more transition metal compounds are well ~ Y~ in
st~h~- -L~c quantities, or in the case of the lithium
compound in an amount slightly greater than
stoichiometrically reguired. The mixing step is
critical hC~c~:~uc~ a poorly mixed reactant powder could
lead to a product having a particle size distribution
range which is too broad b~C~l~c~ the rate of particle
~wLh is ~re~nt upon the ~sr~sion of the lithium
salt.
Suitable lithium _ _~unds are those effective
upon heating to exist in the molten phase with no, or
only partial ~s , -~tion thereof, t~k~ n~ place under
the reaction con~ ~ tions. Such compounds would be
selected from the salts, oxides or hydroxides of
lithium. The preferred lithium ~_ , unds are lithium
hydroxide for ~ ratures below and about 750~C and
lithium carbonates for reaction temperatures above A
750~C. If LiOH is used, thermal ~ - ition of the
LiOH can be controlled without ~on~ _ i tant inhibition
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of the lithiation reaction, by doping the atmosphere
with steam or water vapour.
The transition metal compounds would be
selected from the oxides of cobalt, n~ ~k~l, manganese,
vanadium, iron, titanium, chromium, or mixtures thereof.
Preferably, the transition metal ~- , unds would be
selected from cobalt, ~ckDl or manganese or mixtures
thereof. Alternatively, suitable transition metal
compounds would be selected from the hydroxides,
carbonates or salts of cobalt, nickel, manganese,
vanadium or chromium or mixtures thereof. These latter
transition metal ~_ , unds must be convertable to their
respective oxides in-situ. It is most advantageous i$
the oxide added or produced in-situ is in the same
oxidation state as the final product, so that the
reaction can be carried out with the ~ ni of air or
oxygen, and the stAh~ 1~ 7~tion of the molten lithium salt
can then be effected by co~Al~cting the reaction in an
enclosed atmosphere.
An additive comprising an alkali metal
compound may be added to the reaction mixture.
Preferably, the additive would be selected from NaOH or
KOH. The amount of additive used would range from 0.1
to 50 molar % based on the transition metal content. In
the case of the synthesis of lithium cobalt ~ioY~ ~D
using the pathways described herein, it is not necDcc~y
to add an additive in order to obtain a satisfactory
product. However, in the production of lithium ni ~.kDl
oxide or lithium manganese oxide the prDCDncD of an
additive has been found to assist in opt~ 1 7~ ~g the
kinetics of the reaction and st~h~l~ 7'1 ng the thermal
o~tion of the lithium ~...~o~nd.
The. mixture is intro~ncD~ into a furnace where
it is heated to ~ _~ atures ranging from 200 to 1200~C
for periods of time ranging from lh to 72h. The
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reaction atmosphere, as stated earlier herein, must be
functional to either convert the transition metal
~_ _und to its oxide and/or to maintain the transition
metal oxide in the desired oxidation state, namely that
of the transition metal in the final product. Thus the
atmosphere may be either inert, oY~ 7~ng or r~dl~oing
and is readily de~e~ ~ef1 by one ~k~11e~ in the art.
The product and process of the i-.venLion will
now be described with reffs~e..ce to the following non-
limitative examples.
EXAMPLE 1
The synthesis of lithium cobaltic ~oY~ to
form powders suitable for use in lithium ion battery
~y~ . Having reference to the flowsheet of
Figure l, finely divided lithium carbonate and
cobalt(III) oxide in sto~ ~h~ tric, or slightly greater
than stoichiometric amounts, are ~ YeA in bl~n~ ~ ng
step l. The cobalt (III) oxide may be synth~s~ 7e~ by
various routes as will be described hereinafter. The
mixture is inL~ c~1 into a furnace where it i8 heated
in cAlç~nAtion step 2 to a ~ ,- ature in the range of
about 750 to 900~C in a static, neutral or non-
or~ n~ atmosphere, for a period of time of about 6 h
to 72 h. Following ~Alc~n~tion, the sintered lithium
cobaltic dioxide product is pulverized to break up
agglomerates using a h; - ~ 11 or ball mill in ~ n~
step 3. An optional water wash ~ollows, wA ch~ n~ step 4,
he~A~s~ advd,.~ageously it has been determined that water
appears to l"- -ve most of the soluble impurities such as
sulphur and sodium, as well as unreacted ~Yc~-cc lithium
carbonate.
It is believed that by using an essentially
pure cobaltic oxide powder and lithium carbonate the
process of the invention yields lithium cobaltic
having a constant particle size and surface area,
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irrespective of the shape and size of the reaction
vessel. The physical properties of the powder can be
simply controlled by the furnace temperature and
residence time. Additionally, if an ~Yc~sc of lithium
carbonate is utilized (i.e. a 5 to 10% stoi~h~ stric
~Y~cc over cobalt), then a lithium to cobalt atomic
ratio of 1:1 in the powder product is obtA~ ne~ .
The cobalt (III) oxide can be prepared by
several routes, namely from cobaltic h~Y i ne sulphate
solution or cobaltic pentammine sulphate solution, by
precipitation with sodium or potassium h~dl~xide, or
from a soluble cobalt(II) salt by oxidation with a
strong oxidizing agent, or from cobalt carbonate by high
temperature oxidation in air, or can alternatively be
obt~ineA from ~ -~cial suppliers.
EXAMPLE 2
Preparation of Cobaltic Oxide from Cobaltic ~ ne
Sulphate
72 g of sodium hydroxide (ex 8DH Ltd),
~ccOlved in one litre of water, was slowly added to a
3L solution which contAi n~ 180 g of cobaltic heYr ~ne
sulphate (ex Sherritt Inc), at 90~C. The mixture was
stirred and heated to its ho~ 1 ~ng point, for 30 minutes,
to drive off the copro~ A, The slurry was
cooled and the s~ .atant liquor decanted off. The
black precipitate was wAche~ twice with a similar
quantity of pure water, before it was filtered and
washed twice to 1- ~v~ soluble ~ , ~ties. It was then
dried in an oven at 120~C for about 24 hours. The
product analyzed as hydrated cobaltic oxide with 61.1%
w/w cobalt. The above procedure was repeated twice more
and the product analyzed at 61.5 and 61.3% w/w cobalt.
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12
E~MPLE 3
Preparation of Cobaltic oxide from Cobaltous Sulphate
2.24 kg of . ~um sulphate was ~i-Q~olved in
20 litre_ of aqueous cobaltou~ lp~te solution, with a
cobalt ,v ~- tration of 100 g/L at 50~C. 3.46 kg of
r _ ~ ~ ( as 29% aqueous : - ~) was added slowly, until
any of the in~ ~te precipitate had r~solved.
The resultant cobaltous y~ sulphate solution was
oYid~ed to cobaltic y~ i~ sulphate by the addition
of l.Z8 kg of l~ydL~y~ peroxide (as a 30% solution in
water).
The cobaltic pentammine sulphate solution was
heated to 90~C and 4.2 L aqueous sodium hydroxide (240
g/L) added at a rate of 300 ml/min. The mixture wa_
stirred during this addition and finally heated to its
boiling point to drive off any ~ ~g : ~. The
~y~,..atant liquor was decanted from the settled slurry.
Any soluble 1 _~.ities were ,~ _~ed from the black
precipitate by twice repulping it with pure water,
foll~ ed ~y filtration and ~ Qh~g the filtrate twice
more with pure water. After drying the black solid in
an oven at 120~C for about 24 hours, it analyzed as
hydrated cobaltic oxide with 61.1% w/w cobalt.
EXAMPLE 4
Conversion of Cobaltic Oxide into Lithium Cobaltic
Dioxide over Different Time Periods
1.3 kg of dried cobaltic oxide, y.e~a.el as in
Example 3 above, and 0.9 kg of lithium -~ bo -te (ex
Cyprus Foote) were mixed ~ her in a V hl ~ for 4
hours. 300 g aliquots of the mixture were lo~ded into
one litre CN1000 alumina c~ihl~Q (ex Coors). Each
crucible was heated in a NEY box furnace at 900~C.
Individual crucibles were ,~ ~e-~ after seven different
time periods (1, 3, 6, 12, 24, 36 and 48 hours). The
resultant products were broken up into p~ Q, the size
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13
of a pea, in a mortar and pestle, and fed to a
h- ill, for light deaggl~ ation, and the powder
r~q5 ' Ll~o~yl~ a 400 mesh screen. The minus 400 mesh
fraction was analyzed; the results are given in Table
I. The particle size of the ~ increases as the
r~ time of the reactant mixture in the furnace is
increased, ;~ting that the particles grow in situ.
The surface area of the ~ ~d~L decreased to a constant
value as the particle size increases.
TABLE I
Time (hrs) D 50% (um) Surf2ace Area
m /g
1 3.9 1.73
3 5.2 1.15
6 7.2 0.77
12 8.8 0.45
24 10.9 0.35
36 12.4 0.36
48 15.2 0.38
EXAMPLE 5
Co--ve ~ion of Cobalt Oxide into Lithium Cobaltic D~AJX~
at Different Te~..~atures
A blend of dried cobaltic oxide and lithium
carbonate was mixed as in Example 4. 300 g aliquots
were loaded into one litre CN 1000 alumina crucibles and
placed in the NEY furnace at different temperatures
(800, 900 and 1000~C) for 36 hours. The resultant
products were fed to a hammermill, for light
deagglomeration, and segregated on a 400 mesh screen.
The minus 400 mesh powder was analyzed and the results,
given in Table II, show that the growth of the particles
increases as the furn~ing ~~ ,A~ature increases.
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14
TABLE II
Temp (~C)D 50% (um) Surf~ce Area
(m /g)
800 3.6 0.98
900 12.4 0.36
1000 24.1 0.44
EXAMPLE 6
Comparison of the Synth~-s of Lithium Cobaltic Dioxide
from Cobaltic Oxide and Cobaltous Carbonate
Powders of either cobaltic oxide (prepared as
in Example 2 above) or cobaltous carbonate (ex Aldrich
Chemical) were blended with lithium carbonate, in a V
blender, as in Example 4, and various amounts were
charged to various sizes and -shApe~ of alumina crucible.
The mixtures were each reacted in a NEY furnace for 36
hours at 900~C, and then deaggl~ ated as in ~Y- _l~ 4.
The analytical results are displayed as his~oy~ in
Figures 4 and 5. From Figure 4, it can be seen that the
furnaced product from cobaltic oxide has particles with
a similar median and size range irrespective of the
crucible size, shape or lo~dln~. Figure 5, hcs~v~r,
shows that dioxide made from cobaltous carbonate is
sensitive to crucible size, shape and lo~ . Two
additional runs (52A and 66 in Figure 5) were carried
out in which the cobaltous carbonate was first
~ecc _-~cd before it could react with lithium carbonate,
i.e. the furnace t~mro~ature was first held at 400~C for
6 hours (to ~ ~s~ the carbonate to cobalt oxide) and
then the ~ _ ature was raised to 900~C to _ _l~te the
reaction of the resultant oxide with lithium carbonate.
The analytical results show that crl~c1hle shape and size
do not now appear to affect the particle size of the
lithium cobaltic ~1ox~
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E~U~MPLE 7
The effect of Excess Lithium Carbonate on the
Preparation of Lithium Cobaltic Dioxide.
Mixtures of cobaltic oxide and lithium
carbonate were made up as in ~Y~ 1~ 4, in which the
lithium carbonate content was set at different
stoichiometric ~.D~C~ ( -20%, 0%, 20%, 50% and 100~).
Equal quantities of each mixture were treated in the
furnace as before (900~C for 36 hours). The products
were then analyzed, and the results are given in Table
III. It can be seen that the largest particle sizes are
achieved when an eYc~cc of lithium carbonate is present,
indicating that part~ Ate growth is assisted by the
presence of molten lithium carbonate.
TABLE III
Target (FY~.~CC ~) D 50% (um) Surface Area
(m2/g)
-20 2.6 1.99
~5 12.4 0.36
~20 14.2 0.41
l50 14.2 0.46
+100 11.3 0.63
EXAMPLE 8
The Effect of C- ~~tion on the Preparation of Lithium
Cobaltic Dioxide
Cobaltic oxide and lithium carbonate were
hl~n~, as in F ~ _le 4, and the resultant powder was
sub~ected to _ _~-tion by pl~ ng it in a 2 cm diameter
mold and ~d~ n~ 5 tons of pressure to the piston. The
1 n long ~ t had a density of 1.8 g/cc ~ ~~ed to
0.5 g/cc for the original powder bl~n~e~. Several
comr~cts were pl~c~ in a crucible and placed in a NEY
furnace at 900~C for two different time periods (12 and
24 hours). The products were analyzed, and the results
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16
are given in Table IV. It can be seen that the rate of
growth of the lithium cobaltic dioxide particles
greatly increased when compared to the product from the
original powder. In fact, the compacted product
obt~in~ after 12 hours is similar to that obt~ from
the ~omr~ted powder in 36 hours (Ref. rrable 1).
TABLE IV
Lithium Cobaltic Dioxide made from C~ ted Powder
'rime (hrs) D 50% -400 mesh
(um)
12 13.3
24 13.9
EXAMPLE 9
The synthesis of lithium nickel ~ox~e to form powders
suitable for use in lithium ion battery ~y~te
Having reference to the flowsheet of Figure 1,
lithine, LiOH.H2O, nickel hydroxide, and potassium
and/or sodium hydroxide are ground together and are well
mixed in stoichiometric amounts in bl~n~3~ ng step 1. The
mixture is introduced to a furnace where it is heated
(step 2) in an oxygen ContA ining atmosphere to a
temperature in the range of 500 to 1000~C, for a period
of time of about 10 to 50 hours. Following caiclnation,
the sintered lithium nickel dioxide is optionally
pulverized to break up aggll - ates using a hammermill
or ball mill (step 3). A water wash 4 is carried out
followed by a final oven drying step 5, and
c~ ccification 6 to ~e~;ov2r the lithium n~--k~ x1
powder product.
EXAMPLE 10
Preparation of Lithiated Nickel Dioxide with and without
Potassium Hydroxide
46g of lithine, LiOH.H2O, 93 g of n~Ck~l hydroxide
and 7.3 g of potassium hydroxide (85 % KOH) were ground
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and mixed together in a mortar and a pestle for about 20
minutes. The 1.1:1.0:0.1 (Li:Ni:K) mole ratio blend was
heated in a furnace at 800~C for 20 hours in air, then
was removed from the furnace, pulverized, washed with
distilled water and dried in an oven at 150~C for 5
hours. The resultant product, which r~ ee~ through a
400 mesh sieve, analyzed, by an average particle size of
11.5 microns, and BET (Brl~n~e~-Emmett-Teller) surface
area of 0.74m2/g. After reheating at 600~C for 1 hour,
the surface area was reduced to 0.32 m2/g. ~ ic~l
analysis i n~ ir~ted that the potassium content was 0.002
~ by weight, that is that the potassium _ ,7unds can be
washed out almost completely and that the KOH does not
add impurity ph~Q~s or ~...~o~nds to the final LiNiO2
product.
For _ ,~~ison, a -e~con~ Q~mrl~ of LiNiO2 was
prepared as described above, but without the inclusion
of the potassium hydl~xide. X-ray diffraction ~ n~ c~ted
that LiNiO2 had been obt~; n~, but an SEM mi~l~y a~h
showed that the average particle was about 3.0 microns
which is significantly smaller than the particles
obtained in the presence of KOH, under the same
conditions.
For further comparison, a thlrd sample of
LiNiO2 was prepared as above, but without the inclusion
of the potassium hydroxide and with a larger ~YC~QS of
lithium l.ydl~ide. The starting material corresp~e~
to Li:Ni mole ratio of 1.2:1.0, that is a 20% ~cc
lithium hydroxide, compared to 10% excess lithium
hydroxide in the previous two samples. After heating
the materials at 800~C for 20 hours, it was found that
the particle size was also about 3.0 microns, clearly
trating that the pr~e~nc~ of potassium hydl~ide
is n~ee~y to increase the growth rate of LiNiO2
particles.
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EXAMPLE 11
Preparation and Electrochemical Cell Perfor~nc~ of
Lithiated Nickel Dioxide with Potassium hydroxide at a
Lower Temperature
92g of lithium hydroxide, 185g of nickel
hydroxide and 14.7 of potassium hyd.~xide (85% KOH) were
ground together with a mortar and a pestle for about 20
minutes, the blend heated at 700~C for 20 hours in air,
and the product pulverized then washed with water, and
finally dried in an oven at 150~C. The product which
p~c-s~ through a 400 mesh sieve, analyzed as a single
phase of LiNiO2, with lattice constants a=2.880 A and
b=14.206 A, which agree very well with the reference
data (Journal of Power Sources 54 (1995) 109-114). The
sample particle sizes, as viewed by SEM were between 1
and 3 microns, and an average particle size, as ~ ~ed
by MicrotracTM (light scattering method), of 2.5
microns. t~h~ analysis gave lithium, n l -~k~l and
potassium contents as 7.18% and 59.91% and 0.002% by
weight respectively; the Lheo.etical values for Li and
Ni for LiNiO2 are 7.11% and 60.11%. When impurities due
to the reactants are taken into a~o~--L, the fo. ~1 A for
the product wa~ postulated to be Lil_XNil+xO2 with-
0.02<x<0.02. The value of x in Lil_XNil+XO2 made by
other ~.~v~.~tional methods is usually x>0.02. This
in~in~tes that a better guality product is obt~ne~ with
potassium h~d-~ide in the reaction mixture, probably
because the potassium ~ es better distributlon of
the lithium within the melt at reaction ~ ture.
An electroche ~cal cell, with a cathode,
separator, anode and an electrolyte wa~ ~-- hl ed in
which the cathode was made of the LiNiO2 powder from
above, mixed to a paste, with 9% by weight of Super S
carbon black and 1~ by weight EPDM (ethylene propylene
diene terpolymer), and spread on aluminium foil before
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being allowed to dry; the paste coverage was typ~c~lly
20 mg/cm2 and cathode area was 1.2 x 1.2 cm2. The
electrolyte was 1 M lithium perchlorate, LiCl04 in
propylene carbonate. Lithium metal was used for the
anode and Isotactic Poly~lo~ylene (Celgard 2500TM) as
the separator. Cell hardware was st~i nl q8~ steel with
an aluminium substrate, sealed with an O-ring and stack
pressure provided by a spring. Lithium foil was
att~he~ to the stainless steel hardware and the cathode
att~ch~ to the al~ ~nl substrate. Charge ~ ~--L was
ad~usted to correspond to x-0.5 Li deintercalation in
Li1-_XNil+XO2 during a charge of 20 hours, and the
discharge current ad~usted to correspond to x~0.5 Li
intercalation in 10 hours. The charge voltage was up to
4.15 V and the ~ h~ge voltage down to 3.0 V. Figure
6 shows the first charge and ~ch~ge curve of the cell
using LiNiO2 as cathode materials. The first charge
~-~r~ ty is seen to be 200 mAh/g and the first ~ h~ge
~p~c~ty 145 mAh/g. The cycle life is shown in Figure 7
with voltages between 4.15V and 3.0 V. The fade rates
are very low, and significantly less than materials made
by prior art at this working voltage range and at this
~r~ ty.
Example 12
Preparation of Lithiated Nickel Dioxide with Sodium
~xide
A sample of LiNiO2 was made in the same way as the
first sample in Example 9, with sodium hyd ~ide in
place of the potassium hydroxide: that is, 46g of
lithine, LiOH.H2O, 93 g of n~k~l l.ydlo~ide and 4.5 g
sodium hydroxide (97% NaOH) were ground and ~Ye~
together in a mortar and a pestle for about 20 minutes.
The 1.1:1.0:0.1 (Li:Ni:Na) mole ratio blend was heated
in a furnace at 800~C for 20 hours in air, then was
removed from the furnace, pulverized, w~h~ with
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distilled water and dried in an oven at 150~C for 5
hours. The resultant product, which pA~C~ through a
400 mesh sieve, analyzed by X-ray diffraction as pure
single phase of LiNiO2 with a low sodium content (less
than 5% of the original was left). The X-ray
diffraction pattern of the LiNiO2 product agreed with
the stAn~d data, and no impurity phase was ob~elved.
In conclusion, sodium hydroxide can be used instead of
potassium hyd ~ide ~or this preparation.
F---, le 13
Preparation of Lithiated Cobalt D~Y~ with and without
Potassium Hydroxide
The effect of the potassium hydroxide on the
growth rate of particles during the syn~h~C~ of lithium
cobalt dioxide, LiCoO2 was investigated. Firstly,
LiCoO2 was prepared by the same method as the first
~r _ le of LiNiO2 was prepared in F le 10, that is,
46g of lithine, LiOH.H20, 97g of cobalt oxide
(contA~nin~ 60~ cobalt by weight) and 7.3 g potassium
hydroxide (85 % ROH~ were ground and mixed ~~y~Lher in a
mortar and pestle for about 20 minutes. The 1.1:1.0:0.1
(Li:Co:K) mole ratio blend was heated in a furnace at
800~C for 20 hours in air, then was l~ v~d from the
furnace, pulverized, washed with distilled water and
dried in an oven at 150~C for 5 hours. The resultant
product, which passed through a 400 mesh sieve,
analyzed by X-ray diffraction as a very pure single
phase of LiCoO2. The peak positions agree well with the
st~A~d materials, with lattice constants a~2.819~0.001
A and b=14.07_0.01A. Mi~ ~L~acTM analysis show an
average particle size of 8.5 microns. ~h~ ~ CAl analysis
gave lithium and cobalt of 7.34% and 59.72% by weight, t
very close to 1:1 mole ratio, with a very low potassium
content of 0.031%, showing that the potassium ~ nds
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can be easily washed away after the calcination
reaction.
For l~ ~ison, a second C~mrl~ of LiCoO2 was
made, as above, but without the addition of the
potassium hydroxide, that is, 46g of lithine, LiOH.H20
and 97g of cobalt oxide (cont~ n~ ng 60.5% cobalt by
weight) were ground and mixed together in a mortar and a
pestle for about 20 minutes. The 1.1:1.0 (Li:Co) mole
ratio blend was heated in a furnace at 800~C for 20
hours in alr, then was removed from the furnace,
pulverized, washed with dist1ll~ water and dried in an
oven at 150~C for 5 hours. The resultant product, which
passed through a 400 mesh sieve, analyzed by X-ray
diffraction as a very pure single phase of ~iCoO2 with
lattice constants calculated as a=2.819+0.001 A and
b=14.07+0.01A. Chemical analysis shows lithium and
cobalt ~on~e..ts are 7.58% and 59.17%, re~e~L~vely, that
is the lithium ratio is slightly higher than
stoichiometric requirement. However, the average
particle size was only 4.9 microns, 1n~ ting that
part~ of LiCoO2 prepared with the 10% potassium
hydloxide in the blend grow to be Al L twice as large
as those obt~ n~ without potassium hyd oxlde, under the
same conditions.
Example 14
Dea~qll ation of the Product Particles by W~Sh~ n~ or
Two samples of lithium nickel ~1oY~ were
prepared by a similar method to that outl~ in FYr 1 ~
ll, except that larger crucibles were used, each
containing 500 g of the reactant mixture. The
calcination was carried out at two different
temperatures, 750 and 800~C, with an atmosphere of
o~yy~-- present in the furnace at the lower t , ~ature,
and air instead of o~yye-- at the h~ghD~ t- ,e~ature.
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Two examples of the product ~rom each calcination were
treated as ~ollows. One part was deagglomerated by lightly
grinding in a ceramic ball mill, and the other part was
deagglomerated by simply washing it with water. The median
particle sizes of the resultant powders are given in Table
V for a comparison of median particle size in um of
calcined product after deagglomeration of a mill or with a
simple water wash.
Table V
Median Particle ~ize (um)
750~C with ~2 800~C with air
Water Wash9.7 8.0
Milling 7.4 6.3
Both treatments lead to approximately the same particle
size in the ~inal product, so there is a process choice in
the post treat~ent o~ the calcined product to convert it to
powder: deagglomeration in a mill, or washing with water.
Figure 2 is a photograph of the particles made when lithium
cobalt dioxide (as prepared in Example 4, with 36 h in the
~urnace) is milled to deagglomerate the product particles.
The micrograph shows particles with smooth faceted sur~aces
indicating that the particles comprise one crystal or an
agglomerate of a small number of crystals with an average
diameter in the range o~ 1 to 25 microns as evidenced by
the typical distance between and relative scarcity of grain
boundaries intersecting the particle surfaces. This
characteristic is in contrast to that of particles of
lithium nickel dioxide produced by the methods described in
the prior art which comprise a multi-crystal agglomerate
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~, ,
with a cons~ituent crystal size cf less than 1 micron
consequently having a large number cf grain boundaries
intersecting the particle surfaces and giving the particles
a rough knobbly appearance. Figure 3 is a photograph of
the particles which result from a water wash treatment of
lithium nickel dioxide, as made and treated by the
procedure described in this example. These results clearly
demonstrate that the particles made by the process of this
invention grow in a single step, and that their unique size
and structure do not result from the comminuti~n o~ a large
calcined mass.
It will be understood, of course, that other
embodiments and examples o~ the invention will be readily
apparent to a person skilled in the art, the scope and
purview of the invention being de~ined in the appended
claims.
AMENDED SltEET
