Method of preparing Li.sub.1+X- Mn.sub.2-X O.sub.4 for use as secondary battery

A continuous method of preparing a single phase lithiated manganese oxide intercalation compound of the formula Li.sub.1+x Mn.sub.2-x O.sub.4 comprising the steps of: mixing intimately a lithium hydroxide or a lithium salt and a manganese oxide or a manganese salt; feeding the intimately mixed salts to a reactor; continuously agitating the mixed salts in the reactor; heating the agitated mixed salts in the reactor at a temperature of from about 650.degree. C. to about 800.degree. C. for a time not in excess of about 4 hours in an oxygen-containing atmosphere; and cooling the reacted product to less than about 200.degree. C. in an oxygen-containing atmosphere for a time not in excess of about 2 hours.

FIELD OF THE INVENTION 
This invention relates to a continuous method for the preparation of fine 
powders and/or films of lithium containing ternary oxides. More 
specifically, the present invention relates to the synthesis of Li.sub.1+x 
Mn.sub.2-x O.sub.4 which is an intercalatable compound of interest for 
secondary batteries. 
Heretofore, the lithium containing ternary hydroxides have been prepared by 
mixing the carbonates and oxides of the constituent compounds and heating 
the mixture at high temperatures. Although this method produces battery 
effective material, the lengthy times of reaction and cooling are 
commercially impractical. 
BACKGROUND OF THE INVENTION 
This invention relates to secondary, rechargeable lithium and lithium-ion 
batteries and, more particularly, relates to a continuous method for 
preparing Li.sub.1+x Mn.sub.2-x O.sub.4 intercalation compounds for use as 
the positive electrode in such batteries where x is from about 0 to about 
0.125. 
Lithium-cobalt oxide is currently used as the positive electrode material 
in commercial four-volt lithium-ion cells. On the basis of their lower 
cost, raw material abundance, additional safety, environmental 
acceptability, and electrochemical performance, Li.sub.1+x Mn.sub.2-x 
O.sub.4 intercalation compounds have shown exceptional promise as positive 
electrode materials in such cells. However, for the commecial success of 
Li.sub.1+x Mn.sub.2-x O.sub.4 as a cathode material a process has not 
previously been found that will rapidly and economically produce a 
material with the required electrochemical performance properties. This 
invention addresses this issue. 
LiMn.sub.2 O.sub.4 (Li.sub.1+x Mn.sub.2-x O.sub.4 where x=0) was 
synthesized as early as 1958 D. G. Wickham and W. J. Croft, J. Phys. 
Chem. Solids 7 (1958) 351-360!, by intimately mixing Li.sub.2 CO.sub.3 and 
any manganese oxide, taken in the molar ratio of Li/Mn=0.50, reacting the 
mixture at 800.degree.-900.degree. C. in air, and repeatedly grinding and 
reacting the mixture at this temperature until the sample reached constant 
weight. Acid leaching of LiMn.sub.2 O.sub.4 to produce .lambda.-MnO.sub.2, 
which possesses the LiMn.sub.2 O.sub.4 crystal framework, and the 
subsequent usage of .lambda.-MnO.sub.2 as the positive electrode material 
in a lithium cell were reported by Hunter J. C. Hunter (Union Carbide), 
U.S. Pat. No. 4,246,253, Jan. 20, 1981; J. C. Hunter (Union Carbide), U.S. 
Pat. No. 4,312,930, Jan. 26, 1982; J. C. Hunter, J. Solid State Chem. 39 
(1981) 142-147.!. Hunter electrochemically reduced his .lambda.-MnO.sub.2 
to LiMn.sub.2 O.sub.4, which occurred at 4 V, but they did not cycle his 
cell. He also noted that lithium and manganese compounds other than those 
specified by Wickham and Croft may be used in the synthesis, provided that 
they decompose to lithium or manganese oxides under the reaction 
conditions used. Thackeray, et al. M. Thackeray, P. Johnson, L. de 
Picciotto, P. Bruce and J. Goodenough, Mat. Res. Bull. 19 (1984) 179-187; 
M. Thackeray, L. de Picciotto, A. de Kock, P. Johnson, V. Nicholas and K. 
Adendorff, J. Power Sources 21 (1987)1-8!showed that Li intercalation into 
the LiMn.sub.2 O.sub.4 spinel structure is electrochemically reversible, 
giving two voltage plateaus at .about.4.1 V and 3.0 V vs Li, which 
correspond to the intercalation/de-intercalation of the first and second 
Li ions, respectively, into .lambda.-MnO.sub.2. 
Various investigators studied the synthesis of LiMn.sub.2 O.sub.4 by 
thermal reaction of a lithium and manganese compound, and found it could 
be effected over a large temperature range--i.e., 300.degree.-900.degree. 
C. The ability of the products to intercalate and de-intercalate Li was 
also investigated. The so-called "low" temperature materials, made at less 
than about 550.degree. C., are poorly crystalline, have a distorted spinel 
structure, and cycle at about 3 V but not at 4 V vs Li W. J. Macklin, R. 
J. Neat and R. J. Powell, J. Power Sources 34 (1991) 39-49; T. Nagaura, M. 
Yokokawa and T. Hashimoto (Sony Corp.), U.S. Pat. No. 4,828,834, May 9, 
1989; M. M. Thackery and A. de Kock (CSIR), U.S. Pat. No. 4,980,251, Dec. 
25, 1990; V. Manev, A. Momchilov, A. Nassalevska and A. Kozawa, J. Power 
Sources, 43-44 (1993) 551-559!. These are not the materials of focus in 
this patent application. 
The so-called "high" temperature materials, made at about 
600.degree.-900.degree. C. in an air atmosphere, are quite crystalline. 
They show cycling capability at about 4 V vs Li, but cycle much worse at 3 
V vs Li, losing capacity rapidly J. M. Tarascon, E. Wang, J. K. Shokoohi, 
W. R. McKinnon and S. Colson, J. Electrochem. Soc. 138 (1991) 2859-2868!. 
Even when LiMn.sub.2 O.sub.4 is synthesized at low temperature, as in a 
sol-gel process, it can be cycled in the 4 V regime if it is first 
fired/annealed at high temperatures--e.g., 600.degree.-800.degree. C. P. 
Barboux, F. K. Shokoohi and J. M. Tarasoon (Bellcore), U.S. Pat. No. 
5,135,732, Aug. 4, 1992!. High temperature LiMn.sub.2 O.sub.4 materials 
will be the focus the remainder of this application. 
Investigators have generally found that synthesis of a single-phase product 
in their (static) muffle furnaces required many hours or even days of 
reaction time, which they often coupled with regrinding of the heated 
product and reheating of the reground powder P. Barboux, F. K. Shokoohi 
and J. M. Tarasoon (Bellcore), U.S. Pat. No. 5,135,732, Aug. 4, 1992; W. 
J. Macklin, R. J. Neat and R. J. Powell, J. Power Sources 34 (1991) 39-49; 
A. Mosbah, A. Verbaire and M. Tournoux, Mat. Res. Bull. 18 (1983) 
1375-1381; T. Ohzuku, M. Kitagawa, and T. Hirai, J. Electrochem. Soc. 137 
(1990) 769-775!. Without such laborious synthesis procedures, various 
byproducts are produced in addition to LiMn.sub.2 O.sub.4 --i.e., Mn.sub.2 
O.sub.3, Mn.sub.3 O.sub.4 and Li.sub.2 MnO.sub.3. These substances are 
undesirable in lithium cells, creating low capacities and high fade rates. 
Apart from the production of undesirable byproducts, the synthesis 
parameters also affect the molecular/crystal structure and physical 
properties of the LiMn.sub.2 O.sub.4, and these material properties 
greatly affect the battery capacity and cyclability of the material. 
Momchilov, Manev and coworkers A. Momchilov, V. Manev, and A. 
Nassalevska, J. Power Sources 41 (1993) 305-314! varied the lithium 
reactant, the MnO.sub.2 reactant, the reaction temperature and reaction 
time prior to cooling in air. They found it advantageous to make the 
spinels from lithium salts with the lowest possible melting points and 
from MnO.sub.2 samples with the greatest surface areas. The advantages 
were faster reaction times and more porous products, which gave greater 
capacities and better cyclability (i.e., less capacity fade with cycle 
number). However, the reaction times were the order of days in any case. 
These investigators also found V. Manev, A. Momchilov, A. Nassalevska and 
A. Kozawa, J. Power Sources, 43-44 (1993) 551-559; A. Momchilov, V. Manev, 
and A. Nassalevska, J. Power Sources 41 (1993) 305-314.! that the optimum 
reaction temperature was approximately 750.degree. C. At higher 
temperatures the material lost capacity, presumably due to a decreased 
surface area and from oxygen loss, which reduced some of the manganese in 
LiMn.sub.2 O.sub.4. At the lower reaction temperatures, synthesis required 
even longer times, and evidence of spinel distortion occurred, which 
apparently caused lower capacities. These investigators also demonstrated 
advantage in preheating the reaction mix at temperatures just above the 
melting point of the lithium reactant before reacting at the final 
temperature. 
Tarascon and coworkers J. M. Tarascon, W. R. McKinnon, F. Coowar, T. N. 
Bowmer, G. Amatucci and D. Guyomard, J. Electrochem. Soc. 141 (1994) 
1421-1431; J. M. Tarascon (Bellcore), International Patent Application WO 
94/26666; U.S. Pat. No. 5,425,932, Jun. 20, 1995! found that high capacity 
and long cycle life were best achieved by (1) employing a reactant mixture 
in which the mole ratio of Li/Mn is greater than 1/2 (i.e., 
Li/Mn=1.00/2.00 to 1.20/2.00 so that x in Li.sub.1+x Mn.sub.2-x O.sub.4= 
0.0 to 0.125), (2) heating the reactants for an extensive period of time 
(e.g., 72 h) at 800.degree.-900.degree. C., (3) cooling the reacted 
product in an oxygen-containing atmosphere at a very slow rate, i.e., 
preferably at 2.degree. to 10.degree. C./h, to about 500.degree. C., and, 
finally, (4) cooling the product more rapidly to ambient temperature by 
turning off the furnace. The cooling rate from more than 800.degree. C. to 
500.degree. C. can be increased to 30.degree. C./h if the atmosphere is 
enriched in oxygen. These investigators found that the lattice parameter, 
a.sub.o, of the product was an indicator of the product efficacy in a 
battery, and that a should be less than about 8.23 .ANG.. By comparison, 
for LiMn.sub.2 O.sub.4 made with Li/Mn=1.00/2.00 and with air cooling, 
a=8.247 .ANG.. 
Manev and coworkers V. Manev, A. Momchilov, A. Nassalevska and A. Sato, J. 
Power Sources 54 (1995) 323-328! also found that a Li/Mn mole ratio 
greater than 1.00/2.00 is advantageous to both capacity and cyclability. 
They chose 1.05/2.00 as the optimum ratio. These investigators also found 
that as the amount of pre-mix/reactants in the muffle furnace was scaled 
up from .about.10 g to .about.100 g the capacity decreased significantly. 
This they traced to a depletion of air in the furnace and a resultant 
partial reduction of the product. The problem was alleviated by flowing 
air through the furnace. When the air flow was too great, the capacity of 
the product decreased again, so the air flow had to be optimized to be 
beneficial. Manev and coworkers found the most beneficial cooling rate to 
be several tens of degrees per minute, which is more than 100 times faster 
than that of Tarascon and coworkers. After optimizing all conditions, 
which included the use of lithium nitrate and a very porous chemical 
manganese dioxide as reactants, Manev and coworkers obtained a product 
Li.sub.1+x Mn.sub.2-x O.sub.4 (with x=0.033) that gave a very high 
capacity and low fade rate. The use of lithium nitrate has negative impact 
on the process since poisonous NO.sub.x fumes are expelled during the 
synthesis. When Manev developed a successful synthesis process that 
utilized lithium carbonate rather than lithium nitrate V. Manev, Paper 
given at 9th IBA Battery Materials Symposium, Cape Town, South Africa, 
Mar. 20-22, 1995. (Abstract available)!, this new process once again 
involved a reaction time of several days. 
Howard W. F. Howard, Jr., in Proceedings of the 11th Int'l Seminar on 
Primary and Secondary Battery Technology & Application, Feb. 28-Mar. 3, 
1994, Deerfield Beach, Fla., sponsored by S. P. Wolsky & N. Marincic! 
discussed possible LiMn.sub.2 O.sub.4 production equipment, mainly from a 
cost viewpoint. Although he developed/presented no data, Howard suggesed 
that a roary kiln transfers heat faster than a static oven, which serves 
to shorten reaction times. 
The desirable slow cooling rate coupled with long thermal reaction times is 
very difficult to accomplish on a large scale, as in pilot-plant or 
commercial operation. Therefore, it would be highly desirable to shorten 
the reaction and cooling times while avoiding the unwanted byproducts and 
preserving the needed Li.sub.1+x Mn.sub.2-x O.sub.4 stoichiometry and 
structure, the latter being evidenced by a smaller lattice parameter. 
SUMMARY OF THE INVENTION 
Lithium manganese oxides of the formula Li.sub.1+x Mn.sub.2-x O.sub.4 
(where x is from about 0 to about 0.125) and with lattice parameter of 
about 8.235 .ANG. or less are prepared by mixing a lithium salt/hydroxide 
and a manganese oxide, continuously agitating the mixture while heating in 
an air, oxygen or oxygen enriched atmosphere at a temperature from about 
650.degree. to about 800.degree. C. for about two hours or less, and 
cooling the product in about two hours or less by using similar agitation 
in an air, oxygen or oxygen enriched atmosphere.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention is a continuous method of preparing a single phase 
lithiated manganese oxide intercalation compound of the formula Li.sub.1+x 
Mn.sub.2-x O.sub.4 in which 0.ltoreq.x.ltoreq.0.125 by intimately mixing, 
in stoichiometric amounts, based on the lithium manganese oxide formula, 
lithium hydroxide or a decomposable lithium salt and a manganese oxide or 
decomposable manganese salt; feeding the intimately mixed compounds to a 
reactor; continuously agitating the mixed salts in the reactor; flowing 
air, oxygen or oxygen enriched gas through the reactor; heating the 
agitated mixed compounds in the reactor at a temperature of from about 
650.degree. C. to about 800.degree. C. for a time not in excess of about 
four hours; and preferably not in excess of two hours and cooling the 
reacted product under controlled conditions to less than about 100.degree. 
C. This invention also relates to a method of synthesizing an essentially 
single phase lithium manganese oxide in accordance with the formula 
Li.sub.1+x Mn.sub.2-x O.sub.4 in which 0.ltoreq.x.ltoreq.0.125 and having 
a cubic spinel-type crystal structure. In particular, the invention 
relates to a method of synthesizing such oxide to produce an oxide which 
is suitable for use as a cathode in an electrochemical cell with an anode 
comprising lithium or a suitable lithium-containing alloy. The invention 
also relates to the oxide when produced by the method; and to an 
electrochemical cell comprising said oxide as its cathode. 
According to the invention, a method of synthesizing a lithium manganese 
oxide having a spinel-type crystal structure comprises forming a mixture 
in finely divided solid form of at least one lithium hydroxide or lithium 
salt as defined herein and at least one manganese oxide or manganese salt 
as defined herein, and heating the mixture to a temperature in the range 
of from about 650.degree. C. to about 800.degree. C. to cause said 
compounds to react with each other by simultaneous decomposition to obtain 
said lithium manganese oxide having a spinel-type crystal structure and 
cubic close packed oxygen lattice construction. 
A lithium salt as defined herein means a lithium compound which decomposes 
when heated in air to form an oxide of lithium and, correspondingly, a 
manganese salt as defined herein means a manganese compound which 
decomposes when heated in air to form an oxide of manganese. 
The lithium compound may be a member of the group consisting of LiOH, 
Li.sub.2 CO.sub.3, LiNO.sub.3, and mixtures thereof; the manganese 
compound being a member of the group consisting of MnO.sub.2 (either 
electrolytically or chemically prepared), Mn.sub.2 O.sub.3, MnCO.sub.3, 
Mn.sub.3 O.sub.4, MnO, manganese acetate, and mixtures thereof. Forming 
the mixture may be in a stoichiometric ratio so that there is an at least 
approximate molar ratio of Li:Mn of 1:2, preferably with a slight excess 
of the lithium, i.e. such that the ratio is 1:2.0-1:1.67, preferably 
1:1.94-1:1.82. Forming the mixture may be by mixing in a rotating drum 
mixer, a vibratory mill, a jet mill, a ball mill or the like so long as 
the salts are sufficiently intimately mixed. 
The intimately mixed compounds are then transferred to a hopper, and 
thereby to the reactor by a screw feeder, a pneumatic conveyer, a pulsed 
air jet, or the like. 
The reactor advantageously is a horizontal rotary calciner, a horizontal 
calciner with a rotating screw, a fluidized bed, a heated vibratory 
conveyor belt, or a cascade of vertical rotating hearths. The choice of 
reactor type will be dependent upon the other process parameters and the 
salts used. 
Referring to FIG. 1, in one embodiment of the invention the starting 
material 1 is poured into feed hopper 2. This material falls by the action 
of gravity into a screw conveyor 3 which is used to control the feed rate 
of starting material to the reactor. The screw conveyor 3 discharges the 
starting material into a rotating shell reactor 5. Shell 5 may be rotated 
by any conventional rotating drive means. The solids travel down the 
length of the rotating shell 5, first passing through independently heated 
zones 6a, 6b, 6c surrounded by an outer shell. The solids are discharged 
from the rotating shell 5 through valve 9 into the product drum 10. The 
reactor is airtight in the space between the feed screw conveyor 3 and the 
discharge valve 9, and may be under some positive pressure from the 
atmosphere that comes in contact with the product before it is discharged 
from pipe 8, although as shown in the drawing the pressure in shell 5 is 
substantially atmospheric due to venting through pipe 8 to bag filter 11. 
The optional gas purge inlet pipe 7 allows a counter current flow of air 
or oxygen enriched gas to continuously flow over the reactants. The purge 
gas is vented from the reactor together with the off-gases through pipe 8. 
Drive means for the screw conveyors and rotating shell have not been shown 
since these are well known to those skilled in the art. 
Referring to FIG. 2, the rotating shell 220 optionally has four equally 
spaced lift vanes 210 attached to the inside of the shell. These life 
vanes may be welded or otherwise suitably attached to the inside of rotary 
shell 220. Each of said vanes is spaced equidistantly from its adjacent 
vanes and each extends axially the full length of the rotating shell 220. 
The number of such vanes as well as their size may be varied considerably, 
as long as they function to keep the solids mixed and in intimate contact 
with the atmosphere in the shell. The vanes also aid in moving the solids 
through shell 220. In order to provide further assistance in moving the 
solids downstream through shell 220, the latter may be inclined downward 
in the direction of flow at a slope of up to 1/4 inch per foot of reactor 
length; preferably 1/16 inch per foot. The size of the reactor may be 
varied depending upon the capacity desired. 
The laboratory unit used for the examples consisted of a horizontal rotary 
tube furnace with a 2" diameter and a 3' heating zone. Gas flow rates were 
set between 50 and 500 cc/min. and rotation speed set at 30 RPM. 
The analogous pilot unit consisted of a 6" diameter reactor with 8' of 
heating zones. Gas flow rate was set between 20-40 SCFH. Rotation speed 
was set between 3-10 RPM. 
It is important to keep the reactants agitated during the process. The 
fluidizing motion allows for rapid heat transport and provides 
continuously renewed gas/surface interface exposure. It is this 
combination of conditions that allows the reaction kinetics of the process 
to be greatly enhanced compared to that of the static bed process. 
The heating of the mixture advantageously is in an atmosphere continuously 
purged by a countercurrent flow of air, oxygen or oxygen enriched 
atmosphere to a temperature of from about 650.degree. C. to about 
800.degree. C.; the mixture being held at the maximum temperature, 
preferably with an accuracy of .+-.10.degree. C., for a period of at less 
than about 4 hrs, preferably less than about 2 hrs. The heating step may 
be followed by a cooling step by quenching in air or cooling at the 
natural furnace cooling rate. 
The heating step of the present invention is carried out from about 
650.degree. C. to about 800.degree. C. for a time not in excess of about 
four hours. Preferably the temperature of the heating step is from about 
700.degree. C. to about 750.degree. C. for a time of from about one and 
one-half hours to about 2 hours. 
After the heating step the reactant product advantageously is cooled to 
less than about 200.degree. C. in about two hours or less. Preferably the 
product is cooled to less than about 100.degree. C. and the cooling step 
is performed in less than about one and one-half hours. Where the cooling 
step is performed in one and one-half hours or less the product is 
advantageously annealed by allowing the product to uptake oxygen, thereby 
producing a distortion in the lattice. Where the cooling step is performed 
in about one and one-half hours or less advantageously the cooling is 
performed in at least two zones of progressively cooler temperatures. 
Preferably such cooling takes place in at least three distinct zones, each 
being progressively cooler than the immediately previous zone by at least 
about 90.degree. C. Most preferably the temperatures in the three cooling 
zones are about 725.degree. C., 625.degree. C., and 525.degree. C. 
Li.sub.1+x Mn.sub.2-x O.sub.4 products are characterized analytically in 
various ways, such as by standard chemical and spectroscopic methods to 
give the Li/Mn ratio and the Mn oxidation number. These methods were 
applied to the samples to confirm the formulas that are used to describe 
the materials. 
One of the most useful analytical methods for characterization of these 
materials is x-ray diffraction (XRD), using powder techniques. XRD yields 
two type of useful information, (1) product purity and (2) lattice 
parameter. Since every substance has a unique, well-defined XRD pattern, 
comparison of an XRD pattern with standard patterns determines whether or 
not a single-phase product was obtained. Investigators have found some 
correlation between XRD patterns and battery performance. For example, 
spinels should have a clean LiMn.sub.2 O.sub.4 XRD pattern without 
significant peaks from Li.sub.2 MnO.sub.3, Mn.sub.2 O.sub.3, and Mn.sub.3 
O.sub.4. These materials do not cycle and may do even further harm by 
leaching out of the cathode, causing a breakup of the good material in the 
cathode. 
FIGS. 4, 5, 8 and 9 are clean LiMn.sub.2 O.sub.4 XRD patterns for Samples 
B, C, I and K, respectively. The LiMn.sub.2 O.sub.4 XRD peaks are 
identified by their well-known 2 .theta. positions, which are labeled with 
integers from 501 to 508. These 2 .theta. values can, of course, be 
converted to familiar crystal "d" values by standard methods, with the 
knowledge that the x-radiation was CuK.alpha. radiation. Although the XRD 
patterns appear almost identical for the above named materials, these four 
materials may be differentiated by the way in which they were synthesized, 
which is detailed in Table 1. 
FIGS. 6 and 7 show XRD patterns for spinels contaminated with byproducts. 
The peaks for the major product, Li.sub.1+x Mn.sub.2-x O.sub.4, are 
labeled with the same integers as the corresponding peaks for the pure 
Li.sub.1+x Mn.sub.2-x O.sub.4 in FIGS. 4, 5, 8, and 9. The peaks labeled 
with 700's integers belong to Li.sub.2 MnO.sub.3 and those labeled with 
600's integers belong to either Mn.sub.2 O.sub.3 or Mn.sub.3 O.sub.4 
(these two compounds are difficult to differentiate from a very few small 
peaks). 
The second type of XRD information, i.e., lattice parameter, cannot be 
obtained from visual inspection of the scans as shown in the figures. 
Rather, specialized techniques of "lattice parameter refinement," familiar 
to those skilled in the art of crystallography and XRD, very accurately 
examines the exact location of all the peaks, and from this information, 
calculates the best cubic spinel unit cell dimension on the 
crystallographic "a" axis; this is the lattice parameter, a.sub.o. 
Various investigators have shown that the lattice parameter can be a very 
diagnostic tool, as it often correlates directly with capacity fade rate, 
which is the decrease in discharge capacity with cycle number. The lattice 
parameter varies with the stoichiometry of the cubic Li-Mn spinel (i.e., 
with x in Li.sub.1+x Mn.sub.2 O.sub.4) and with the degree of oxidation of 
the spinel. Li.sub.1.00 Mn.sub.2.00 O.sub.4 has a lattice parameter of 
a.sub.o =8.2476 .ANG., (Standard X-ray Diffraction Powder Patterns, 
Section 21--Data for 92 Substances, by M. C. Moris, H. F. McMurdie, E. H. 
Evans, B. Paretzkin, H. S. Parker, W. Wong-Ng, D. M. Gladhill and C.R. 
Hubbard, National Bureau of Standards, U.S., Monograph 25, 21 78 (1984)). 
The value of a.sub.o decreases with Li removal (oxidation), attaining a 
value of 8.03 .ANG. for the cubic Mn.sub.2 O.sub.4 (.lambda.-MnO2) phase. 
As lithium is added to LiMn.sub.2 O.sub.4 (x&gt;0 in Li.sub.1+x Mn.sub.2-x 
O.sub.4), the manganese becomes more oxidized and a.sub.o decreases to 
about 8.2 .ANG. J. M. Tarascon, W. R. McKinnon, F. Coowar, T. N. Bowmer, 
G. Amatucci and D. Guyomard, J. Electrochem. Soc. 141 (1994) 1421-1431!, 
and the capacity fade rate of the spinel decreases. The additional lithium 
and manganese oxidation causes a decrease in discharge capacity, the 
theoretical maximum 4-V discharge capacity being (1-3x) lithium 
ions/electrons per molecular unit of Li.sub.1+x Mn.sub.2-x O.sub.4, as 
being determined by the highest theoretical Mn oxidation number being 
4.00. 
Samples of the lithium manganese oxide prepared in accordance with the 
described techniques were formed into positive secondary cell electrodes 
by intimately mixing with a small amount of graphite (10 to 40% by weight) 
and a binder (.about.5% by weight) to form a cathode mix; pressing this 
cathode mix onto a conductive backing; and then drying this 
cathode-mix/backing assembly (called the positive electrode) by heating in 
a dry gas stream. These electrodes were then tested in the usual manner in 
flat electrochemical test cells. One type of such cell is a demountable 
cell shown in FIG. 3. The cells were assembled in a dry argon atmosphere 
using the Li.sub.1+x Mn.sub.2-x O.sub.4 --containing positive electrode 
301 with a conductive backing 302 separated from a lithium foil negative 
electrode 303 with stainless steel conductive backing 304 by porous glass 
fiber and/or polypropylene and/or polyethylene separator papers 305 and 
306 saturated with an electrolyte comprising a mixture of 1 molar lithium 
hexafluorophosphate (LiPF.sub.6) in a 50/50 wt/wt solution of ethylene 
carbonate (EC) and dimethyl carbonate (DMC). These active cell components 
were pressed into intimate contact such as to be insulated from the 
atmosphere. In the demountable cell of FIG. 3, this was accomplished by 
the two flat cylindrical cell halves 307 and 308 that made up the cell 
body. The two polypropylene pieces, between which the active cell sandwich 
was placed, were drawn together with bolts (not shown in FIG. 3) to press 
the cell components together. A polypropylene-polyethylene "O" ring 309 
around the periphery of this cell between the two cylindrical halves 307 
and 308 both served to seal the cell from electrolyte escape or air entry 
and to take the excess pressure of the bolts once the cell components were 
drawn together. The two cell halves were constructed with metal bolts 
sealed into their centers 310 and 311, such that these bolts conducted the 
current into and out of the active cell components. O-rings also were used 
to ensure a tight seal around the current collector bolts 312 and 313. The 
bolts were held firmly against the "O" rings with nuts 314 and washers 
315. 
The test cells were then evaluated to determine the behavior of cell 
voltage during charge-discharge cycles as a function of the change in 
lithium content per formula unit during the progressive reversible 
transformation of Li1+xMn.sub.2-x O.sub.4. When charging is initiated 
(i.e., with cell voltage.about.3.1-3.5 volts), the manganese begins to 
oxidize and lithium ions transport out of the Li.sub.1+x MN.sub.2-x 
O.sub.4 through the electrolyte and into the lithium foil. The process 
proceeds until a voltage of 4.3 volts is reached, a potential at which 
most of the lithium atoms have been transferred to the lithium anode. The 
cell was then discharged to 3.0 volts and recharged many times at a rate 
of 0.5 mA/cm.sup.2 of cathode area. Two such charge and discharge cycles 
are shown in FIG. 10. 
The cell passed roughly 120 milliamp hours of charge per gram of active 
cathode material, Li.sub.1+x Mn.sub.2-x O.sub.4, for each half cycle. This 
quantity of charge decreased with cycle number, as is typical for any 
battery system. This decrease, termed cycle fade, is one of the most 
important battery performance features of cathode materials, along with 
the initial discharge capacity. The maximum discharge capacity for the 
cell was recorded. This usually was the discharge capacity on the first 
cycle, although for a small fraction of the cells, the capacity maximized 
on the second or even the third cycle. The fade rate for the cell was 
calculated as the least squares slope of the line through the graph of 
discharge capacity vs. cycle number after 30 and 50 cycles (see FIG. 11). 
This slope, in milliamp hours per gram of Li.sub.1+x Mn.sub.2-x O.sub.4, 
was converted to fade rate in percent capacity loss per cycle by dividing 
the slope by the initial discharge capacity and multiplying by 100. 
Spinels were synthesized by the proposed process in a pilot-scale rotary 
kiln (reactor). Spinels were also synthesized by various other published 
or patented processes, for comparison with those made by the proposed 
process. These methods included (a) standard laboratory procedures, i.e., 
thermal reaction in a muffle furnace followed by cooling in the ambient 
atmosphere, (b) standard laboratory procedures but with slow cooling 
(which employed a computerized controller on the furnace), and (c) air 
cooling followed by special annealing at 850.degree. C. and then very slow 
cooling (10.degree. C./h) to 500.degree. C. or room temperature. Syntheses 
were also conducted in the pilot reactor with various modifications, for 
the purpose of evaluating various processing parameters. 
It is well known that during the "very slow cool/anneal" step in air or an 
oxygen enriched atmosphere, the spinel absorbs oxygen into the crystal 
lattice. This phenomena can be observed by monitoring the weight increase 
using Thermal Gravimetric Analysis (TGA). 
Using the slow cooling process in accordance with the invention, the 
cooling rate can be greatly increased if the spinel material is allowed to 
be continuously agitated. This provides a much greater exposure of 
solid/gas interfaces. In addition, the continuous purging of air or oxygen 
allows for a continuous availability of oxygen at the surface interface 
for rapid absorption into the lattice. 
As the examples will show, the capacity and rate of cycle fade for the 
spinel made by the proposed process were about equivalent to those for 
spinels made by the optimum previously discussed laboratory processes, 
which involve many hours or even days of heating and cooling time. On the 
other hand, when the laboratory processes were performed for just a few 
hours, comparable to the times employed with the proposed methods, the 
capacities were substantially lower and, in some cases, the fade rates 
were higher. 
Numerous samples were evaluated so as to lend credence to correlations. 
Each sample has been battery cycled in replicate tests, so as to provide 
the uncertainty in each test. Thus, differences in capacities and fade 
rates are subject to statistical examination. The description of how the 
materials were made is given in Table I and all mean results and standard 
deviations (.sigma.) are shown in Table II. 
Most of the important features of the claimed process are explained here by 
pairwise comparisons of tests (as opposed to a linear multiple regression 
of all data). When pairwise comparisons are made, it is desirable to keep 
all parameters constant except for the one under investigation. For 
example, when comparing different heat/cooling treatments, it desirable to 
compare the same material. Also, if comparing different materials for a 
given compositional difference (e.g., ratio of lithium to manganese), it 
is desirable that the materials are made from the same precursor EMDs and 
lithium compounds. This has been done as far as possible. All the example 
spinels are synthesized from Kerr-McGee Chemical Corporation alkaline 
battery grade EMD, which has very repeatable specifications. Materials 
synthesized from the same lithium compound--i.e., either lithium hydroxide 
or lithium carbonate--were compared where possible. 
EXAMPLE 1 
The examples of the invention are as good as or better than any other 
materials tested. The process used for the invention examples consisted of 
reaction in the rotary kiln under air for .about.2 h, cooling in a rotary 
kiln under air for .about.2 h, and manufactured with excess lithium--i.e., 
Li/Mn.sub.2 =1.05 (rather than Li/Mn.sub.2 =1.00). The examples of the 
invention are Samples B and C. These two samples were identically 
processed except that the cooling was done in a small laboratory rotary 
kiln (after first reheating the sample to 725.degree. C.) and under an 
atmosphere of O.sub.2 in the case of Sample B, whereas the sample was 
zone-cooled in the pilot kiln under air in the case of Sample C. Table lI 
shows that B and C exhibit adequate discharge capacities and the lowest 
fade rates (or equivalent thereto) in the table. Furthermore, their XRD 
patterns (FIGS. 4 AND 5) are clean and lattice parameters are among the 
lowest lattice parameters. 
In particular, the examples of the invention are as good as materials made 
by long laboratory routes (static bed furnace), which involve 20 h 
reaction time and either: (a) 12 h cooling times (60.degree. C./h), termed 
"laboratory-slow-cooling," or (b) treatment that involves annealing the 
sample above 800.degree. C. and cooling very slowly, i.e., at 10.degree. 
C./h, termed anneal/very slow cool!. Specific comparisons from Table II 
are: 
a. B & C (invention) vs H (the "same" pilot material but anneal/very slow 
cool!after synthesis) shows that the invention material is as good as, if 
not better than, the material that was annealed/very slowly cooled!. 
b. Sample I is a laboratory-prepared sample with precursors and composition 
equivalent to those of the invention samples, but Sample I received 
anneal/very slow cool! treatment. Material I is no better, on the 
average, than B & C. The 50-cycle fade rate of I and the capacity are 
statistically equivalent to those of the other two, because the standard 
deviation for the "I" values are so great. Sample I produced a clean XRD 
pattern (FIG. 8). 
c. Sample K is equivalent to B & C in precursor and composition, but K was 
reacted for 20 h in the laboratory static furnace and then 
"laboratory-slow-cooled" rather than given anneal/very slow cool! 
treatment. Sample K, although one of the best materials, is no better than 
B & C in capacity and fade rate. The XRD pattern for K is clean (FIG. 9). 
d. Sample L' is a pilot material made from Li.sub.2 CO.sub.3 and then given 
anneal/very slow cool! treatment. (The parallel anneal/very slow cooled! 
sample, H, was made from LiOH). No inventive example was made from 
Li.sub.2 CO.sub.3. However, Sample O is a laboratory prepared sample that 
is identical to L', except that it was laboratory-slow-cooled. Sample O is 
as good as Sample L', indicating that the anneal/very slow cool! 
treatment is no improvement over reaction at 725.degree. C. followed by 
laboratory-slow-cooling. 
e. Sample G is a pilot material that was synthesized equivalently to L', 
but reheated and laboratory-slow-cooled. Sample G exhibits a lower fade 
rate than L', indicating, as in (d), that the anneal/very slow cool! 
treatment may even be inferior to 725.degree. C. followed by 
laboratory-slow-cooling. 
g. Samples I vs I' and J vs J' indicate that anneal/very slow cool! 
treatment of materials prepared at 725.degree. C. improves the 
performance. 
EXAMPLE 2 
The present invention shows in Table II that (1) the rotary kiln with air 
flow allows reaction times of only .about.2 h, whereas reaction in a 
static furnace for 2 h gives a completely unsuitable product and (2) a 
reaction time of .about.20 h in a static laboratory furnace is required to 
yield the same effect as .about.2 h reaction in a rotary kiln with air. 
For this example, air cooling was employed, as laboratory-slow-cooling 
would, in effect, lengthen the reaction time from 2 h and confound the 
test. 
a. Sample M was synthesized in the static furnace for just 2 h and then air 
cooled. This process contaminated the material with deleterious 
byproducts, as the XRD scan shows. The initial capacity is only 76.8 
mAh/g, and two of four cells assembled would not even cycle 10 times. 
These problems are due to the high level of impurities. This material is 
completely unsuitable as a battery cathode. The comparable starting 
material, made from LiOH with Li/Mn.sub.2 =1.00 but reacted 20 h in the 
static furnace, is Sample N. This material exhibited a good XRD pattern 
and initial capacity, although the fade rate is mediocre by the standards 
of the good materials. No material was made in rotary kilns with 
Li/Mn.sub.2 =1.00. 
b. Samples A and F are two materials that were started from equivalent 
pre-mixes and then reacted in the rotary kiln with air flow, followed by 
air cooling. Sample I', equivalent in precursors and composition to A and 
F, was made in the static/lab furnace with reaction time =20 h. The rotary 
samples (A & F), are as good in both discharge capacity and fade rate as 
the material reacted for 20 h in the lab furnace (I'). This example and 
2.a indicate that the 2 h reaction in the rotary kiln is about equally 
effective to that in the static furnace at 20 h, and would be 
substantially more effective than 2 h reaction in a static furnace. 
c. Three samples from equivalent (Li.sub.2 CO.sub.3) precursor and of 
equivalent composition are: E (made in the static laboratory furnace with 
only 2 h reaction time and then air cooled), L (made in the pilot rotary 
kiln with 2 h reaction time and then air cooled, and J' (made in the 
static laboratory furnace with 20 h reaction time and then air cooled). 
The E process resulted in contaminated material (cf XRD pattern of FIG. 7) 
and has a somewhat low discharge capacity (112 mAh/g). J' also showed a 
somewhat low capacity, although its XRD pattern was clean. L, the pilot 
sample, showed the best capacity of the three, and also had a clean XRD 
pattern. The fade rates were mediocre to poor in all cases, although, 
surprisingly, the 2 h laboratory sample showed the best fade rate. 
EXAMPLE 3 
An oxygen containing gas in the rotary is necessary for the inventive 
process. This is shown in Table II by Sample D, which was made with 
N.sub.2 flowing through the kiln during the reaction and cooling. The 
capacity is unacceptably low (101 mAh/g), corresponding to the 
contaminated XRD scan (FIG. 6). The fade rate also is mediocre to poor. 
The comparable sample with air in the rotary kiln is L, which shows an 
acceptable capacity and clean XRD scan, proving its superiority over D. 
The fade rate of L is comparable to that of D, although the fade rate of L 
operates from a higher capacity. Results for invention examples B and C 
show that either oxygen or air atmosphere is satisfactory. 
EXAMPLE 4 
The inventive process of slow/zone cooling in the rotary kiln (2 h) is 
advantageous. As shown in Table II, this is demonstrated by comparing 
Samples B and C, which are so-cooled, with Sample A, which is the 
identical premix and reaction product but air cooled. Samples B and C show 
significantly better capacities and especially fade rates than A. 
EXAMPLE 5 
Table II shows that in the inventive process a Li/Mn.sub.2 ratio greater 
than 1.00 is beneficial. No sample was made and cooled in the rotary kiln 
for which Li/Mn.sub.2 ratio=1.00; i.e., there was no direct comparison 
with Samples B and C. This is because it had been previously established, 
with laboratory synthesized materials, that there was a definite benefit 
with excess lithium. Therefore there was no need to produce poorer 
materials in the pilot plant. Above (1.c) we showed that "inventive" 
synthesis was as good as the best laboratory synthesis, the latter being 
20 h reaction time and laboratory-slow-cooling (i.e., 60.degree. C./h or 
12 h cooling). Therefore, when the best laboratory materials are shown to 
be superior to materials that are identical except that Li/Mn.sub.2 =1.00, 
it may be inferred that pilot (inventive process) materials with 
Li/Mn.sub.2 &gt;1.00 would be better than the inventive process materials 
with Li/Mn.sub.2 =1.00. 
Sample K, which is equivalent to inventive process materials B and C, is 
compared to K', which is equivalent except that Li/Mn.sub.2 =1.00. Sample 
K' shows a greater capacity than K, which is anticipated from theory. 
However, the capacity of K is still great enough to be suitable. In fade 
rate, which is the needed feature, Sample K is much superior to Sample K'. 
By inference, inventive process materials should be better than rotary 
materials with Li/Mn.sub.2 =1.00. 
Table I 
Sample Preparations and Descriptions 
Sample A: Pilot material. Li/Mn.sub.2 =1.05. LiOH/EMD reacted@725.degree. 
C. in rotary kiln with air for 2 h. Air cooled. 
Sample B: Sample A reheated to 725.degree. C. in lab rotary kiln and slow 
cooled therein under O.sub.2 to ambient@300.degree. C./h. 
Sample C. Pilot material. Sample A zone cooled in pilot rotary kiln under 
air, which required 2 h. 
Sample D. Pilot material. Li/Mn.sub.2 =1.05. Li.sub.2 CO.sub.3 /EMD reacted 
in rotary kiln@725.degree. C. with N.sub.2 for 2 h. Air cooled. 
Sample E. Lab material. Li/Mn.sub.2 =1.05. Li.sub.2 CO.sub.3 /EMD reacted 
in static furnace@725.degree. C. for 2 h. Air cooled. 
Sample F. Pilot material. Li/Mn.sub.2 =1.05. LiOH/EMD reacted@725.degree. 
C. in rotary with air for 2 h. Air cooled. 
Sample G. Pilot material. Li/Mn.sub.2 =1.05. Li.sub.2 CO.sub.3 reacted in 
rotary@725.degree. C. with air for 2 h. Air cooled. Reheated to 
725.degree. C. and slow cooled in static lab furnace at 60.degree. C./h. 
Sample H. Pilot material. Sample B reheated in static lab furnace to 
850.degree. C. and cooled to room temperature very slowly (i.e., at 
10.degree. C./h). 
Sample I'. Lab material. Li/Mn.sub.2 =1.05. LiOH/EMD reacted@725.degree. C. 
in static furnace for 20 h. Air cooled. 
Sample I. Lab material. Sample I' reheated in static furnace to 850.degree. 
C. and cooled to 500.degree. C. very slowly (i.e., at 10.degree. C./h), 
and then furnace turned off for quick cooling to room temperature. 
Sample J'. Lab material. Li/Mn.sub.2 =1.05. Li.sub.2 CO.sub.3 /EMD 
reacted@725.degree. C. in static furnace for 20 h. Air cooled. 
Sample J. Lab material. Sample J' reheated in static furnace to 850.degree. 
C. and cooled very slowly (at 10.degree. C./h) to 500.degree. C., and then 
furnace turned off for quick cooling to room temperature. 
Sample K. Lab material. Li/Mn.sub.2 =1.05. LiOH/EMD reacted@725.degree. C. 
for 20 h in static furnace. Then slow cooled to room temperature at 
60.degree. C./h. (Note: this "lab slow cooling" is much faster than 
Bellcore cooling of 10.degree. C./h). 
Sample K'. Lab material. Li/Mn.sub.2 =1.00. LiOH/EMD reacted@725.degree. C. 
in static furnace for 20 h. Then "lab-slow-cooled" to room temperature at 
60.degree. C./h. 
Sample L: Pilot material. Li/Mn.sub.2 =1.05. Li.sub.2 CO.sub.3 /EMD 
reacted@725.degree. C. in rotary kiln with air for 2 h. Air cooled. 
Sample L'. Pilot material. Sample L reheated to 850.degree. C. in lab, 
static furnace and cooled therein@10.degree. C./h to room temperature. 
Sample M. Lab material. Li/Mn.sub.2 =1.00. LiOH/EMD reacted in static 
furnace@725.degree. C. for 2 h. Air cooled. 
Sample N. Lab material. Li/Mn.sub.2 =1.00. LiOH/EMD reacted in static 
furnace@725.degree. C. for 20 h. Air cooled. 
Sample O. Lab material. Li/Mn.sub.2 =1.05. Li.sub.2 CO.sub.3 /EMD reacted 
in static furnace@725.degree. C. for 20 h. The 
"lab-slow-cooled"--i.e.,@60.degree. C./h. 
TABLE II 
__________________________________________________________________________ 
Lattice Parameter 
Mean Capacity, 
Mean Face, % per Cycle .+-. 
.sigma. 
Sample 
XRD Scan (.ANG.) mAH/g .+-. .sigma. 
30 Cycles 
50 Cycles 
n* 
__________________________________________________________________________ 
A Clean LiMn.sub.2 O.sub.4 pattern 
8.2402 112 
.+-. 13 
0.38 .+-. 0.05 
0.29 .+-. 0.03 
2 
B Clean LiMn.sub.2 O.sub.4 pattern 
8.2342 117.1 
.+-. 0.4 
0.24 .+-. 0.04 
0.22 .+-. 0.019 
2 
C Clean LiMn.sub.2 O.sub.4 pattern 
8.2344 126 
.+-. 5 
0.26 .+-. 0.02 
0.20 .+-. 0.01 
2 
D Pattern includes significant Li.sub.2 MnO.sub.3 & Mn.sub.3 O.sub.4 
peaks 8.2550 101 
.+-. 3 
0.80 .+-. 0.12 
0.47 .+-. 0.04 
3 
E Pattern includes significant Li.sub.2 MnO.sub.3 & Mn.sub.3 O.sub.4 
peaks 8.2468 112 
.+-. 1.6 
0.42 .+-. 0.09 
0.34 .+-. 0.04 
4 
F Clean LiMn.sub.2 O.sub.4 pattern 
8.2466 129.7 
.+-. 0.7 
0.41 .+-. 0.04 
0.31 .+-. 0.03 
3 
G Clean LiMn.sub.2 O.sub.4 pattern 
8.2397 119.7 
.+-. 6.1 
0.37 .+-. 0.06 
0.30 .+-. 0.06 
6 
H Clean LiMn.sub.2 O.sub.4 pattern 
8.2302 122.5 
.+-. 0.2 
0.24 .+-. 0.02 
0.23 .+-. 0.03 
2 
I Clean LiMn.sub.2 O.sub.4 pattern 
8.2338 121.0 
.+-. 8.5 
0.33 .+-. 0.10 
0.25 .+-. 0.08 
2 
I' Clean LiMn.sub.2 O.sub.4 pattern 
8.2340 115 
.+-. 6 
0.37 .+-. 0.12 
0.34 .+-. 0.15 
2 
J Clean LiMn.sub.2 O.sub.4 pattern 
8.2407 123.9 
.+-. 5.7 
0.65 .+-. 0.03 
0.46 .+-. 0.05 
2 
J' Clean LiMn.sub.2 O.sub.4 pattern 
8.2440 113.1 
.+-. 1.0 
0.72 .+-. 0.13 
0.67 .+-. 0.08 
3 
K Clean LiMn.sub.2 O.sub.4 pattern 
8.2338 115 
.+-. 11 
0.27 .+-. 0.14 
0.23 .+-. 0.07 
5 
K' Clean LiMn.sub.2 O.sub.4 pattern 
8.2450 132 
.+-. 9 
0.61 .+-. 0.07 
0.47 .+-. 0.03 
5 
L Clean LiMn.sub.2 O.sub.4 pattern 
8.2400 119.6 
.+-. 3.9 
0.70 .+-. 0.09 
0.47 .+-. 0.02 
4 
L' Clean LiMn.sub.2 O.sub.4 pattern 
8.2457 131.6 
.+-. 1.0 
0.53 .+-. 0.08 
0.39 .+-. 0.01 
2 
M Pattern includes significant Li.sub.2 MnO.sub.3 & Mn.sub.3 O.sub.4 
peaks -- 76.8 
.+-. 1.7 
0.35 (2 cells 
3ailed 
to charge) 0.22 
N Clean LiMn.sub.2 O.sub.4 pattern 
8.2467 124.6 
.+-. 3.3 
0.60 .+-. 0.035 
0.45 .+-. 0.037 
3 
O Clean LiMn.sub.2 O.sub.4 pattern 
8.2407 110 
.+-. 7 
0.41 .+-. 0.09 
0.38 .+-. 0.08 
3 
__________________________________________________________________________ 
*n = Number of cells tested.