Method of making lithium battery electrode compositions

Fine particles of vanadium oxide or lithiated vanadium oxide are less than 100 microns in size and on the order of 30 microns in size. Such fine particles are prepared by spray-drying a precursor mixture. Such oxide particles are also intermingled with fine particles of carbon by including carbon particles in the precursor mixture.

FIELD OF THE INVENTION 
This invention relates to electrochemical batteries and more particularly 
to improved positive electrode material for use with lithium-containing 
negative electrodes. 
BACKGROUND OF THE INVENTION 
Current batteries contain high surface area transition metal oxide active 
material such as vanadium oxide powders. These oxide powders are obtained, 
for example, by milling of vanadium oxide material. Current methods for 
the manufacture of powders involve mechanical grinding of vanadium oxide 
material prepared, for example, by rapid quench of molten material or by 
precipitation from an aqueous solution. As a result, the vanadium oxide is 
in the form of lumps or large particles. By standard milling techniques it 
is difficult to reduce the lumps to a size less than 100 micrometers 
(microns) and extremely difficult to achieve a particle size closer to 10 
microns. Smaller vanadium oxide particle sizes are desirable because the 
larger the surface area, the higher is the current drawn from a battery 
while the current density on the surface of the vanadium oxide active 
material remains low which allows high utilization of the active material. 
A typical coarse V.sub.2 O.sub.5 powder of 95% purity available from 
Fisher Scientific Company, has a median particle size of about 110 microns 
and a surface area of about 5 meters.sup.2 /gram. Such a powder would need 
extensive milling. 
Another problem posed by transition metal oxide active material is that it 
is necessary to add carbon to the composite cathode. The requirement for 
carbon and the amount thereof depends, to some extent, on the specific 
oxide. The electronic conductivity of vanadium oxides decreases 
substantially (2-4 orders of magnitude) during lithium insertion upon 
discharge of a battery. This increases the need for even greater amounts 
of added carbon. Methods which allow reduction of the carbon content are 
important in order to increase the specific energies of the battery. 
SUMMARY OF THE INVENTION 
According to one aspect of the invention, very fine particles of an oxide 
of vanadium, represented by the nominal general formula V.sub.2 O.sub.5, 
are prepared by first forming a wet mixture comprising at least one 
volatile constituent and vanadium pentoxide, and then spray-drying the wet 
mixture. Spray-drying is preferably conducted using pressure nozzles which 
cause atomization by forcing the wet mixture under pressure at a high 
degree of spin through a small orifice. The wet mixture is thereby 
dispersed into fine droplets and dried by a relatively large volume of hot 
gasses sufficient to evaporate the volatile constituent, thereby providing 
very fine particles of the oxide of vanadium, nominally V.sub.2 O.sub.5, 
having a size on the order of 100 microns or less. Desirably, particles of 
a median size less than about 50 microns are produced. It is preferred 
that the particle size be 30 microns or less and closer to 10 microns or 
less. It should be noted that median particle size refers to that size at 
which 50% by weight of the particles are, respectively, above and below in 
size. 
Preferably, the volatile constituent is water and spray-drying takes place 
in an air stream. The temperature of the air at the outlet is preferably 
greater than 100.degree. C. The inlet air stream is at an elevated 
temperature sufficient to remove a major portion of the water with a 
reasonable dryer volume, for a desired dry powder production rate and 
size. Air inlet temperature, droplet size and air flow rate are key 
factors which affect particle size and density of the product. 
According to another aspect of the invention, there is provided a method 
for preparing an electrode material comprising fine particles of vanadium 
oxide and carbon. In this embodiment, the wet mixture comprising the 
volatile constituent(s) and an oxide of vanadium also includes fine 
particles of carbon. The oxide of vanadium is preferably represented by 
the general formula V.sub.2 O.sub.5. The wet mixture is spray-dried as 
generally described above. The carbon particles are dispersed in the wet 
mixture and maintained in dispersion when the wet mixture is ejected from 
the orifice. 
According to another aspect of the invention, fine particles of 
lithium-vanadium oxide of the nominal general formula LiV.sub.3 O.sub.8 
are prepared by forming a wet mixture comprising at least one volatile 
constituent, lithium hydroxide (LiOH) and an oxide of vanadium represented 
by the general formula V.sub.2 O.sub.5. The LiOH is reacted with the 
V.sub.2 O.sub.5 for a time and at a temperature sufficient to provide the 
lithium-vanadium oxide, LiV.sub.3 O.sub.8. Desirably, the reaction takes 
place at a temperature of at least about 20.degree. C.; and preferably in 
a range of about 20.degree. C. to 60.degree. C. It is desired that the 
LiOH be present in an amount sufficient to provide at least 1 mole of Li 
atoms for each 1.5 moles of the V.sub.2 O.sub.5. Once the reaction to form 
LiV.sub.3 O.sub.8 is completed, the mixture containing the LiV.sub.3 
O.sub.8 product is spray-dried as generally described above with regard to 
V.sub.2 O.sub.5. This results in LiV.sub.3 O.sub.8 being in the form of 
particles having a median size less than about 100 microns. Desirably, 
particles of a median size less than 50 microns are produced, and 
preferably 10 to 30 microns or less. 
If desired, prior to spray-drying, the wet mixture may also include fine 
particles of carbon dispersed therein. The carbon may be added either 
before or after the reaction to form LiV.sub.3 O.sub.8 takes place. Upon 
spray-drying, the product contains fine particles of LiV.sub.3 O.sub.8 
intermingled with the fine carbon particles. 
Advantageously, the invention provides very fine particles of vanadium 
oxide or compounds thereof with or without carbon particles. The fine 
particles of the oxide powder are advantageously obtained in their 
preferred size, while minimizing formation of agglomerates which render 
such powders less effective for use as a cathode active material. 
It is an object of the invention to provide electrodes of improved specific 
energies by reducing vanadium oxide particle size and by improving contact 
between oxide particles and conductive carbon of the electrode. Other 
objects include reducing cost of production, reducing or eliminating 
milling and increasing consistency and purity of the electrode active 
material. 
These and other objects, features and advantages will become apparent from 
the following description of the preferred embodiments and accompanying 
drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As shown in the drawing, an electrochemical cell or battery 10 has a 
negative electrode side 12, a positive electrode side 14, and a separator 
16 therebetween. In accordance with common usage, a battery may consist of 
one cell or multiple cells. The negative electrode is the anode during 
discharge, and the positive electrode is the cathode during discharge. The 
negative electrode side includes current collector 18, typically of 
nickel, iron, stainless steel, and/or copper foil, and a body of negative 
electrode active material 20. The negative electrode active material 20 is 
sometimes simply referred to as the negative electrode. The positive 
electrode side includes current collector 22, typically of aluminum, 
nickel, iron, stainless steel, and/or copper foil, or such foils having a 
protective conducting coating foil, and a body of positive electrode 
active material 24 which has as its main component one or more oxides of 
vanadium. The positive electrode active material 24 is sometimes simply 
referred to as the positive electrode. The separator 16 is typically a 
solid electrolyte, electrolyte separator. A suitable electrolyte separator 
(polymer electrolyte) is described in U.S. Pat. No. 4,830,939 incorporated 
herein by reference. The electrolyte separator is a solid organic polymer 
matrix containing an ionically conducting liquid with an alkali metal salt 
and the liquid is an aprotic polar solvent. 
In one embodiment, a cathode active material of the general formula V.sub.2 
O.sub.5 (vanadium pentoxide) is prepared in powder form. The fine 
particles of the powder are of a size on the order of 100 microns or less. 
The powder is prepared by first forming a mixture comprising at least one 
volatile constituent and an oxide of vanadium represented by the nominal 
general formula V.sub.2 O.sub.5. The mixture is spray-dried thereby 
providing fine particles of the oxide of vanadium, less than 100 microns, 
desirably, less than 50 microns, and preferably, less than 10 microns. 
If desired, carbon particles are dispersed in the mixture before 
spray-drying so as to provide fine particles of carbon intermingled with 
the vanadium oxide. The process of spray-drying facilitates dispersion of 
and an intermingling of the oxide and carbon constituents in the final 
product, and prevents coagulation of the constituents so as to maintain 
the product in the form of a very fine powder having fine particles of 
both carbon and oxide less than 100 microns, desirably less than 50 
microns, and preferably less than 10 microns. 
In the process of the invention, water is preferably the volatile 
constituent to be removed, although the wet mixture may include other 
components. It is known that 1 gram of vanadium pentoxide (V.sub.2 
O.sub.5) dissolves in about 125 milliliters of water. With lesser amounts 
of water, a viscous liquid or gel is formed. Such low water content gels 
are known as "xerogels". 
During the process, water is removed or separated from the oxide in a 
stream of hot gas. Preferably, the volatile constituent is water and 
spray-drying takes place in an air stream. The temperature of the air at 
the outlet is preferably greater than 100.degree. C. The inlet air stream 
is at an elevated temperature sufficient to remove a major portion of the 
water with a reasonable dryer volume, for a desired dry powder production 
rate and size. Air inlet temperature, droplet size and air flow rate are 
key factors which affect particle size and density of the product. 
The equipment necessary to accomplish spray-drying depends on the quantity 
of material being spray-dried. In an experiment described below, an 
Anhydro lab model spray-dryer was used which is capable of drying up to 
about 7.5 kg of water per hour. This Anhydro spray-dryer dried 14 liters 
of the wet mixture using an air flow rate of 125 m.sup.3 /hour with a 
temperature drop of about 150.degree. C. The spray-drying reduced the 
moisture content to the order of 1% to 10% by weight, while producing an 
oxide product in the form of particles having a size of about 20 microns. 
To further ensure that small particle size is achieved during the 
spray-drying process, it may be desirable to place the precursor materials 
in a sieve and filter them to first remove large particles. This ensures 
that carbon particles, which do not dissolve in water, are of a 
sufficiently small size in the final product. 
The solid content of the aqueous mixture was in the range of 100 grams to 
200 grams of vanadium pentoxide solid per 400 ml of water. When carbon is 
included, the solid content (carbon and V.sub.2 O.sub.5) is adjusted to 
provide about 5 parts V.sub.2 O.sub.5 for each 1 part carbon. 
A more specific discussion of the spray-drying process follows below with 
respect to the LiV.sub.3 O.sub.8 oxide product. Similar conditions apply 
to both the LiV.sub.3 O.sub.8 and V.sub.2 O.sub.5 products. A discussion 
of the general background of spray-drying may also be found in Perry's 
"Chemical Engineer's Handbook", 4th Edition, published by McGraw Hill. 
The spray-drying method of the invention was used to prepare LiV.sub.3 
O.sub.8 in a completely amorphous state with and without carbon. The 
amorphous state is beneficial for rate capabilities and energy density. 
This composite is prepared by forming the aqueous V.sub.2 O.sub.5 mixture, 
as described above and including LiOH in the mixture. The amount of 
V.sub.2 O.sub.5 and LiOH correspond to the stoichiometric amounts of the 
two compounds needed for formation of LiV.sub.3 O.sub.8. It is thought 
that part of the V.sub.2 O.sub.5 dissolves in solution, followed by 
reaction between the dissolved V.sub.2 O.sub.5, LiOH and water and then 
with the remaining solid V.sub.2 O.sub.5, with the subsequent formation of 
LiV.sub.3 O.sub.8. The reaction is fairly slow at room temperature, on the 
order of 10.degree. C. to 40.degree. C., and typically around 20.degree. 
C. The reaction proceeds at a reasonable rate at about 50.degree. C. to 
60.degree. C. A process of adding progressive amounts of vanadium 
pentoxide to an LiOH solution is more fully described in U.S. Pat. No. 
5,039,582 which is incorporated in its entirety by reference. The 
LiV.sub.3 O.sub.8 product typically forms a very fine precipitate. 
In the experimental method of this invention, following preparation of 
V.sub.2 O.sub.5, the V.sub.2 O.sub.5 is added to the LiOH solution. If the 
V.sub.2 O.sub.5 is added sufficiently slowly, it is clearly dissolved. The 
initial suspension of the powder is seen as particles which gradually 
disappear and the solution then becomes clear. 
The LiV.sub.3 O.sub.8 prepared according to the stated procedure may 
actually be a fine powder, but because of the high concentrations used, it 
appears as a high viscosity liquid, cream, or gel. It is this liquid which 
is used for spray-drying. Similar liquids of V.sub.2 O.sub.5 are also 
formed. The two types of liquids are similar. The V.sub.2 O.sub.5 is 
called a xerogel and it is the gel which gave this type of material their 
group name, xerogel. The particle size probably depends on the viscosity 
of the liquids. Lower viscosity probably result in smaller particles after 
atomization. A typical composition used for the formation of LiV.sub.3 
O.sub.8 is as follows: 400 ml H.sub.2 O; 12 g LiOH (=0.5 mol); 136.5 g 
V.sub.2 O.sub.5 (=0.75 mol). 
In various experiments, the LiOH was dissolved in the water and heated to 
about 50.degree. C. The V.sub.2 O.sub.5 was then added gradually over a 
period of 2-30 minutes. The rate of adding the V.sub.2 O.sub.5 did not 
seem to affect the result. Similarly, the temperature had been varied 
between approximately 50.degree. C. and 85.degree. C. without any notice 
effect. It is probably possible to prepare the LiV.sub.3 O.sub.8 gel even 
when the concentrations of LiOH and V.sub.2 O.sub.5 are reduced to one 
third of the amounts given above. Similarly, it is possible to increase 
the concentration about a factor of 4, but in this case, the resulting 
material is practically solid. Smaller particle sizes are expected at 
lower concentrations; however, the correlation between viscosity and the 
initial composition is not well-known. 
The aqueous mixture containing the LiV.sub.3 O.sub.8 product was then 
spray-dried, with the objective of achieving as small a particle size and 
as low a water content as possible. There was used approximately 14 liters 
of the amorphous LiV.sub.3 O.sub.8 in water. The solid content was 
measured to be between 15% and 20% by weight. 
The experiment equipment used was as follows: 
______________________________________ 
Laboratory spray-dryer: 
No. 1 - by Anhydro* 
Feeding system: Peristaltic pump 
Atomizer: Centrifugal atomizer, type 
CD63 
Wheel diameter: 63 mm 
Heating system: Electrical 
Drying chamber: Conical. All powder to the 
cyclone 
Chamber diameter: 1.000 mm 
Powder separation: 
Cyclone 
Amount of dry air: 
125 m.sup.3 /h 
______________________________________ 
*APV Pasilac Anhydro A/S is represented in the U.S. by: 
APV Crepaco Inc. 
Dryer Division 
165 John L Dietsch Square 
Attleboro Falls, Massachusetts 02763 
Anhydro makes spray dryers in many sizes, the above-described unit is known 
as a laboratory spray-dryer, and it can dry (remove) up to 7.5 kg of water 
per hour. The unit was used to dry approximately 14 liters of amorphous 
LiV.sub.3 O.sub.8 in water. The solid content was measured to be between 
15 and 20 weight percent. The parameters which could be varied on the unit 
were: atomizer type, inlet temperature, air feed rate and liquid feed 
rate. In this case, the atomizer was a centrifugal type (50,000 RPM) and 
the air flow was fixed. The operating conditions were set to achieve 
particle size as small as possible, and the operating conditions were 
chosen for that. The material was stirred continuously before feeding into 
the spray-drier. This was necessary to maintain a homogeneous suspension. 
The start-up went smoothly, and a steady-state operation was achieved with 
a inlet air stream temperature of approximately 280.degree. C. and a 
liquid feed rate, which gave an outlet air temperature of approximately 
120.degree. C. Interestingly, the product temperature never exceed the 
outlet temperature. Sample of the product, which was a fine powder, 
contained 2.2 weight percent and 8.6 weight percent of water, as shown in 
Table 1. The total process time for the 14 liters was approximately 3 
hours, but the operation was stopped twice, once because of the need to 
position a magnetic bar in one of the batches, and once because of 
inadequate cleaning during the shut-down. 
A rough mass-balance on the final product indicated that approximate 40% or 
more of the material was lost due to handling, but more significantly 
because some of the particles were too small to be stopped by the cyclone. 
This makes it necessary to use a bag-filter (or additional cyclones). 
Despite this, very small particle size was achieved. 
TABLE 1 
______________________________________ 
Experimental Results 
______________________________________ 
Run number 1 2 
Time min 90 90 
Feed product kg 8 8 
Dry material in 
% 19.6 19.6 
feed product 
Atomizer speed rpm 15000 15000 
Inlet temperature 
.degree.C. 
280 280 
Outlet temperature 
.degree.C. 
129 129 
Amount of powder 
kg 0.78 0.66 
Remaining moisture 
% 2.2 8.6 
Bulk density, pressed 
g/ml 0.81 0.73 
Bulk density, unpressed 
g/ml 1.04 0.97 
Particle size, .mu.m 26 20 
RRB average diameter 
Particle size, n 2.4 2.6 
standard deviation 
______________________________________ 
The particle sizes are measured by laser diffraction, type Malvern. The 
amount of dry material in the feed product was measured by heating with an 
infra red lamp system at 105.degree. C. for 30 minutes. Approximately, 50% 
of the powder has passed through the cyclone due to the small particle 
size and was lost. A filter is, therefore, needed after the cyclone. 
If desired, prior to freeze-drying, carbon particles are dispersed in the 
aqueous solution either before or after reaction to form LiV.sub.3 O.sub.8 
takes place. Preferably, the reaction to form LiV.sub.3 O.sub.8 is 
conducted while keeping the carbon and undissolved V.sub.2 O.sub.5 
dispersed in solution, so that the contact between the product LiV.sub.3 
O.sub.8 and the carbon is optimized. Advantageously, because part of the 
V.sub.2 O.sub.5 is dissolved during the procedure, intimate mixing between 
the V.sub.2 O.sub.5 precursor (from which the LiV.sub.3 O.sub.8) is formed 
and the carbon is essentially automatically achieved. 
Carbon particles may be obtained from Noury Chemical Corporation, under the 
designation Ketjen Black. The Ketjen Black particles, in an as-received 
condition, have a BET surface area of approximately 900 m.sup.2 /gram. 
Ketjen Black has an average or median particle size or equivalent average 
diameter in the range of about 10 to about 100 nanometers (0.01 to 0.1 
microns), and typically in the order of 30 nanometers. Thus, the carbon 
particles and oxide particles are very fine and of micron or submicron 
size. 
The product of the method of the invention is essentially in the form of 
carbon particles coated with the vanadium oxide or lithium-vanadium oxide 
(LiV.sub.3 O.sub.8) or, depending on the relative sizes of the carbon 
particles and the vanadium oxide particles, the oxide particles may be 
coated with carbon. In any event, intimate mixing and intimate contact 
between carbon grains and oxide grains is achieved by the method of the 
invention. Thus, the advantages of this procedure are that there is 
improved grain-to-grain contact between carbon and vanadium oxide 
particles (V.sub.2 O.sub.5 or LiV.sub.3 O.sub.8), and also between the 
various carbon particles, which enhances the electric contacts in the 
carbon and vanadium oxide network of the composite electrode. 
The vanadium oxide active materials (V.sub.2 O.sub.5 or LiV.sub.3 O.sub.8) 
of the invention were used to prepare cells with lithium-based anodes. 
Several cells were prepared by mixing oxide active material, carbon 
(typical Shawinigan Black) and electrolyte/binder. The oxides were 
prepared with and without carbon. Thus, in some cases, carbon particles 
were added after fine particles of the oxide active material had been 
formed. Typical cathode constituents are as given in Table 2. 
TABLE 2 
______________________________________ 
Percent by 
Typical Cathode Composition 
Weight 
______________________________________ 
Vanadium Oxide (V.sub.2 O.sub.5 or LiV.sub.3 O.sub.8) 
49% 
Carbon 11% 
Propylene Carbonate (PC) 28% 
PolyEthylene Oxide (PEO) 1% 
PolyEthyleneGlycolDiAcrylate (PEGDA) 
9% 
TriMethylPolyEthylene Oxide TriAcrylate 
2% 
(TMPEOTA) 
______________________________________ 
The weight ratio carbon/active material, used in conventional batteries, is 
approximately 1:10. An objective is to reduce the ratio and it is actually 
preferred to have no carbon. However, a lower limit target is a range of 
3-15 weight percent carbon relative to the active material. A typical 
cathode contains about 10 weight percent carbon, 50 weight percent active 
material and the remaining material is then binder and electrolyte. The 
invention permits one to raise the content of the active material to about 
65 weight percent. A higher content is desired, but with the presently 
used materials and manufacturing techniques, a target upper limit for 
combined carbon and active material is in the range 70-80 weight percent 
of the cathode composition. 
The cathode is coated onto nickel foil followed by electron beam curing 
(cross-linking/polymerization) of the acrylate component. Then the 
electrolyte is coated on top of the cathode and cured with ultraviolet 
light. The lithium electrode is applied on top of the electrolyte 
separator and the battery is finally placed in a flexible pouch which is 
heat sealed under vacuum. 
The energy density of the batteries based on these new electrode materials 
with smaller oxide particles is improved. This is believed to be achieved 
by decreasing carbon content of the cathode, providing better contact 
between the carbon and the vanadium oxide. The lesser carbon content 
compared to what would otherwise be required, is due to the increased 
contact which increases the electronic conductivity allowing higher 
current drains, while the energy density remains essentially unchanged. 
The method of the invention eliminates, or at least reduces, the need for 
standard milling techniques, which reduce particle size to less than 100 
microns and which it is difficult to reduce particle size to about 50 
microns. Since suitable particle size, less than 50 microns, is achieved 
by intimate mixing with carbon to form an electronically conducting carbon 
network with good contact to the active material on a microscopic scale, 
the invention avoids heavy-duty milling methods. However, if desired, 
milling of the final product is possible because the degree of milling is 
lessened. That is, the mixing force of any subsequent milling step would 
be very much be reduced. 
While this invention has been described in terms of certain embodiments 
thereof, it is not intended that it be limited to the above description, 
but rather only to the extent set forth in the following claims. 
The embodiments of the invention in which an exclusive property or 
privilege is claimed are defined in the appended claims.