Title: Manganese, bismuth mixed metal oxide cathode for rechargeable lithium electrochemical systems
Abstract: The present invention provides a manganese bismuth mixed metal oxide cathode material through a solid-state reaction between manganese dioxide, and either bismuth or a bismuth compound in a compound having the general formula MnOy(Bi2O3)x, which affords charge transfer catalytic behavior that allows the cathode to be fully reversible at suppressed charge potentials and increased discharge potentials. The MnOy(Bi2O3)x cathode material may be incorporated into an electrochemical cell with either a lithium metal or lithium ion anode and an organic electrolyte. The present invention provides a compound with the general formula MnOy(Bi2O3)x, where subscript x is between 0.05 and 0.25, subscript y is about 2 and the overcharge protection is not needed as the subscript z approaches 0.0. In the preferred embodiment, a cathode material where subscript x is between 0.05 and 0.135 with the formula MnO2(Bi2O3)0.12 provides the much-needed full reversibility, high voltage stability and reduced charge transfer impedance. A manganese bismuth mixed metal oxide cathode for an lithium electrochemical system, a lithium electrochemical system and a rechargeable lithium battery employing the same compound with the general formula MnOy(Bi2O3)x and methods for making manganese bismuth mixed metal oxide cathode material for lithium electrochemical devices having the general formula MnOy(Bi2O3)x are also provided.
Patent Number: 7,011,908 Issued on 03/14/2006 to Atwater, et al.
| Inventors:
|
Atwater; Terrill B. (North Plainfield, NJ);
Salkind; Alvin J. (Princeton, NJ);
Suszko; Arek (Lakewood, NJ)
|
| Assignee:
|
The United States of America as represented by the Secretary of the Army (Washington, DC)
|
| Appl. No.:
|
684063 |
| Filed:
|
October 8, 2003 |
| Current U.S. Class: |
429/224; 429/218.1; 429/232; 252/518.1; 252/519.13; 423/599; 423/594.7 |
| Current Intern'l Class: |
H01M 4/50 (20060101) |
| Field of Search: |
429/224,218.1
252/518.1,519.13
423/599,594.7
|
References Cited [Referenced By]
Other References
Atwater et al. "Thermodynamic and kinetic study of the Li/MnO2 Bi2O3 electrochemical
couple". Journal of the Electrochemical Society, vol. 145, No. 3, Mar. 1998, pp. L31-L33.
Atwater et al. "Electrochemical properties of the Li/MnO2 Bi2O3 couple", Proceedings
of the Power Sources Conference (1998), 38th.
|
Primary Examiner: Weiner; Laura
Attorney, Agent or Firm: Zelenka; Michael, Tereschuk; George B.
Goverment Interests
GOVERNMENT INTEREST
The invention described herein may be manufactured, used, imported, sold, and
licensed by or for the Government of the United States of America without the payment
to me of any royalty thereon.
Claims
We claim:
1. A method of making a manganese mixed metal oxide cathode, comprising the steps of:
selecting a bismuth compound from the group of bismuth compounds consisting of
Bi
2O
3, Bi(OH)
3 or Bi metal;
mixing said bismuth compound with MnO
2;
heating said mixture in an annealing oven between 400° C. and 600°
C. for at least 72 hours;
forming a positive, active manganese bismuth mixed metal oxide compound having
the general formula MnO
y (Bi
2O
3)
x,
where said subscript x is greater than 0.05 and less than 0.25 and said subscript
y is about 2.0;
drying said compound; and
forming said cathode by mixing said compound with a conductive carbon and a binder.
2. The method of making the manganese mixed metal oxide cathode, as recited in
claim 1, further comprising the step of combining said compound, said carbon and
said binder in a 87:9:4 weight percent.
3. The method of making the manganese mixed metal oxide cathode, as recited in
claim 2, wherein said compound results from a solid-state reaction between manganese
dioxide; and said bismuth compound.
4. The method of making the manganese mixed metal oxide cathode, as recited in
claim 3, wherein said subscript x is greater than 0.05 and less than 0.135.
5. The method of making the manganese mixed metal oxide cathode, as recited in
claim 4, wherein said compound is MnO
2 (Bi
2O
3)
0.12.
Description
FIELD OF THE INVENTION
This invention relates in general to the field of electrochemical power sources
and in particular to rechargeable lithium batteries and rechargeable lithium-ion
batteries using a manganese bismuth metal oxide or mixed metal oxide as the positive
electrode or cathode.
BACKGROUND OF THE INVENTION
Portable batteries with increased energy and power densities are required
as the use of portable electronic equipment rapidly continues to increase. Batteries
are typically the limiting factor in the performance of most portable commercial
and military electronic equipment due to the restrictions on the size, weight and
configuration imposed on the equipment by limitations from the power source. In
some cases, safety and environmental factors are also significant considerations
for deploying a particular power source. Lithium batteries provide high energy
density, conformal packaging and improved safety, which make them one of the most
promising electrochemical systems under development today.
Lithium batteries use high valence metal oxide materials, which are reduced
during the electrochemical reaction. This reaction in rechargeable lithium and
rechargeable lithium ion batteries must be fully reversible in order to have a
viable cell. Common reversible metal oxide materials used in lithium batteries
include: Li
xMn
2O
4, Li
xCoO
2
and Li
xNiO
2. These materials remain reversible against lithium
whenever the lithium subscript "x" is maintained between 0.15 and 0.90 for Li
xMn
2O
4
and 0.4 and 0.95 for Li
xCoO
2 and Li
xNiO
2.
However, if the stoichiometry exceeds these limitations, the material undergoes
a phase change and is no longer reversible. The primary consequences of this phase
change of the material and subsequent irreversibility are that the cell will no
longer accept a charge, which makes the cell inoperable. In order to maintain this
stoichiometry rigid electronic control in employed, but rigid controls such as
current and voltage limiters employed at the stack level and are often not practical
for many situations where lithium batteries are deployed, which makes maintaining
reversibility even more critical for those lithium electrochemical systems used
in portable electronic devices and apparatus.
Thus there has been a long-felt need to solve the problems associated with maintaining
reversibility in lithium batteries without suffering from the disadvantages, limitations
and shortcomings associated with rigid stoichiometry electronic control and phase
change. It has been found that a mixed metal oxide that introduces bismuth into
the manganese dioxide cathode structure yields a material with high voltage stability
and a reduced charge transfer impedance due to catalytic activity. This reduced
charge transfer impedance provides a lower potential charge mechanism avoiding
the problems associated with loss of reversibility in lithium batteries without
suffering from the disadvantages, limitations and shortcomings associated with
rigid stoichiometry electronic control and phase change.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a manganese bismuth mixed
metal oxide cathode material as the positive electrode in rechargeable lithium
and lithium ion electrochemical cells.
Another object of the present invention is to provide a manganese bismuth
mixed metal oxide cathode material having the general formula MnO
y (Bi
2O
3)
x
as the positive electrode in rechargeable lithium and lithium ion electrochemical cells.
It is still a further object of the present invention is to provide a manganese
bismuth mixed metal oxide cathode material having the general formula MnO
y
(Bi
2O
3)
x as the active positive electrode where
subscript x is between 0.05 and 0.25 and subscript y is about 2.
It is yet another object of the present invention is to provide a manganese bismuth
mixed metal oxide cathode material having the formula MnO
2 (Bi
2O
3)
0.12
as the positive electrode in rechargeable lithium and lithium ion electrochemical cells.
It has now been found that these and the aforementioned objects can now be advantageously
attained by reacting metallic bismuth or a compound containing bismuth with MnO
2.
Manganese based mixed metal oxides with bismuth were initially examined as a cathode
material for rechargeable lithium and lithium-ion batteries in order to provide
a new mixed metal oxide cathode material as the positive electrode in rechargeable
lithium and lithium ion electrochemical cells. A stable mixed metal oxide was fabricated
through a solid-state reaction between manganese dioxide, and bismuth or a bismuth
compound. The electrochemical reaction is:
Li+MnO
y(Bi
2O
3)
x=Li
zMnO
y(Bi
2O
3)
x
which is reversible when the lithium subscript "z" in this reaction is between
0.0 and 0.50. Further, overcharge protection is not required due to the stability
of the material as the lithium subscript z approaches 0.0. In preferred embodiments,
subscript x is between 0.05 and 0.135. It is anticipated that the MnO
y
(Bi
2O
3)
x materials, cathodes and cells of the
present invention will also provide inexpensive and less costly lithium and lithium
ion electrochemical cells, without suffering from the disadvantages, shortcomings
and limitations of prior art devices. The devices and methods of the present invention
provided much improved sustained specific capacity of about 120 mAhrs/g, and the
material exhibited an inherent catalytic behavior for charge transfer.
The present invention also encompasses a single step method for making manganese
bismuth mixed metal oxide cathode material for lithium electrochemical devices
having the general formula MnO
y (Bi
2O
3)
x
as the active positive electrode where subscript x is between 0.05 and 0.25
and subscript y is about 2. The single-step method for making a cathode material
for a lithium electrochemical system, comprises forming a mixture by mixing the
manganese oxide and bismuth metal or bismuth oxide. The mixture is then heat treated
in an annealing oven.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 depicts spectra of MnO
2 (Bi
2O
3)
0.06
after heat treatment showing the formation of unwanted Bi
2Mn
4O
10
and the decomposition product Mn
2O
3;
FIG. 2 is a chart illustrating comparative discharge curves the typical cyclic
profile for lithium-bismuth manganese mixed metal oxide electrochemical button cell;
FIG. 3 is a chart illustrating the typical cyclic profile for lithium-bismuth
manganese mixed metal oxide electrochemical button cell;
FIG. 4 is a chart illustrating comparative high charge rate capability of the
lithium-bismuth manganese mixed metal oxide electrochemical couple; and
FIG. 5 is a chart showing specific capacity and number of cycles of a MnO
2(Bi
2O
3)
compound of the present invention.
DETAILED DESCRIPTION OF THE DRAWINGS
The manganese bismuth mixed metal oxide material of the present invention advantageously
provides cathode materials answering long-felt needs for a fully reversible lithium
battery without suffering from any of the drawbacks, limitations and disadvantages
of prior art phase changing batteries. In order to resolve the reversibility problem,
electrochemical measurements were performed on rechargeable lithium batteries using
a manganese, bismuth mixed metal oxide as the positive electrode. Initial efforts
concentrated on a primary Li/Bi
xMnO
2 system, which showed
an increased operating voltage when compared to Li/βMnO
2. These
measurements identified an increased discharge potential for the Li/Li
xMnO
2(Bi
2O
3)
y
electrochemical couple and suppressed charge potentials for the Li/Li
xMnO
2(Bi
2O
3)
y
compound. Changes in cell behavior as a function of bismuth stoichiometry
in MnO
2, as well as cell discharge and charge properties with respect
to the bismuth stoichiometry, were also measured. Preliminary results indicated
that MnO
y (Bi
2O
3)
x electrochemical
cells would produce the required reversibility and still meet other necessary lithium
battery operational objectives, without suffering from the setbacks, limitations
and disadvantages associated with prior art lithium batteries. Subsequent efforts
have yielded an improved solid-state reaction process for rechargeable Li/MnO
y
(Bi
2O
3)
x systems. The mixed metal oxide
materials, cathodes and cells showed a reversible couple between lithium and the
mixed metal oxide.
The present invention provides a manganese bismuth mixed metal oxide cathode
material through a solid-state reaction between manganese dioxide, and either bismuth
or a bismuth compound in a compound having the general formula MnO
y
(Bi
2O
3)
x. This MnO
y (Bi
2O
3)
x
compound affords charge transfer catalytic behavior that allows the cathode
to be fully reversible at suppressed charge potentials and increased discharge
potentials. The MnO
y (Bi
2O
3)
x cathode
material of the present invention is incorporated into an electrochemical cell
with either a lithium metal or lithium ion anode and an organic electrolyte. In
all embodiments, the cathode of the present invention comprises a compound with
the general formula MnO
y (Bi
2O
3)
x,
where subscript x is between 0.05 and 0.25, preferably between 0.05 and 0.135,
subscript y is about 2 and the overcharge protection is not needed as the subscript
z approaches 0.0 in this reaction:
Li+MnO
y(Bi
2O
3)
x=Li
zMnO
y(Bi
2O
3)
x
which provides charge transfer catalytic behavior allowing the cathode to be
fully reversible. In the preferred embodiment, a cathode material where subscript
x is between 0.05 and 0.135 with the formula MnO
2 (Bi
2O
3)
0.12
provides the much-needed full reversibility, high voltage stability and reduced
charge transfer impedance. The materials, cathodes and cells of this invention
answer the long-felt need for a reversible cathode for rechargeable lithium batteries
without suffering from the shortcomings, limitations and disadvantages of rigid
stoichiometry electronic control, phase change and loss of reversibility.
Referring now to the drawings, FIG. 1 shows the X-ray diffraction spectra
for MnO
2 (Bi
2O
3)
0.06 after heat treatment.
The starting material for this process is Bi(OH)
3 precipitated on MnO
2.
The data show the formation of unwanted Bi
2Mn
4O
10 and
the decomposition product Mn
2O
3. Decomposition of MnO
2
is initiated at 400° C. and the formation of Bi
2Mn
4O
10
is initiated at 600° C.
FIG. 2 is a chart showing comparative discharge curves for a single Li/Bi
0.27MnO
2
cell. The data show the capacity achieved when the cell is subjected to a charge
discharged cycle of 4.0, 2.0 and 1.0 mA, respectively. These discharge curves show
the second and third full cycle for each current with 4.0 mA represented by the
thin line, 2.0 mA represented by the broken line and 1.0 mA represented by the
bold line. The high coulombic efficiency for this couple, 99 percent for these
cycles, is displayed clearly in the data presented in FIG. 2. The data also show
reasonable rate capability for this non-rate optimized cell design. The cell components
are not under compression and have a long electrode-to-electrode distance.
FIG. 3 is a chart showing the 70
th through 80
th charge
and discharged cycles discharge for a Li/MnO
2 (Bi
2O
3)
0.12
cell. This plot is typical for this electrochemical couple. As with the FIG.
2 chart, the FIG. 3 data show the high coulombic efficiency for this electrochemical
couple. Data showing the high charge rate capability of the lithium-bismuth manganese
mixed metal oxide electrochemical couple is plotted in FIG. 4.
FIG. 4 is a chart showing the high charge rate capability of the lithium-bismuth
manganese mixed metal oxide electrochemical couple. FIG. 4 depicts comparative
high charge rate curves of a 1 mA discharge with a 4 mA charge for 6.72 hours,
which is represented by the thin line, and a 1 mA discharge with a 1 mA charge
for 15.7 hours, which is represented by the bold line.
These charts and drawings clearly show that a stable manganese, bismuth mixed
metal oxide can be fabricated for use as a rechargeable lithium battery cathode.
The initial specific capacity of the Li/MnO
2 (Bi
2O
3)
0.12
cathode material was found to be 150 mAhr/g. This capacity was maintained
with 2/3 of the initial discharge capacity through 100 cycles. Additionally, the
system exhibited a coulombic efficiency greater than 97 percent and a 95 percent
energy efficient charge. A number of other variations are also possible, including
the manganese, bismuth mixed metal oxide resulting from a solid-state reaction
between manganese dioxide and bismuth the cathode material, providing a sustained
specific capacity of about 120 mAhrs/g, the subscript x being between 0.05 and
0.135 and the compound being fully reversible. The compound could be MnO
2
(Bi
2O
3)
0.12. Also, the cathode material
can be placed in a rechargeable system or a lithium ion electrochemical system.
The cathode material can maintain the initial specific capacity with 2/3 of an
initial discharge capacity through 100 cycles, provide a coulombic efficiency greater
than 97 percent and a 95 percent energy efficient charge. The cathode material
can be produced from this solid-state reaction:
Li+MnO
y(Bi
2O
3)
x=Li
zMnO
y(Bi
2O
3)
x
where the subscript z approaches 0.0, an overcharge protection is avoided and
a charge transfer catalytic behavior is provided that allows the cathode material
to be fully reversible. The cathode material can also be produced from a solid-state
reaction between manganese dioxide, and a bismuth compound.
FIG. 5 is a chart showing specific capacity and number of cycles of a MnO
2
(Bi
2O
3) compound of the present invention; compared to current
state of the art rechargeable MnO
2. The data shows despite a lower initial
capacity the capacity of MnO
2 (Bi
2O
3) compound
of the present invention maintains a greater capacity as compared to current state
of the art MnO
2 over 50 cycles.
In addition to cathode material for a lithium electrochemical system embodiment,
the present invention also contemplates other embodiments, which include a manganese
bismuth mixed metal oxide cathode for a lithium electrochemical system, a lithium
electrochemical system with a metal oxide cathode and a rechargeable lithium battery.
Many of the variations to the cathode material embodiment also apply to these embodiments.
The Bi
xMnO
2 material is prepared through a series of solid-state
reactions. Bismuth is introduced into the MnO
2 matrix by mixing Bi
2O
3,
Bi(OH)
3 or Bi metal with MnO
2 and heating in a furnace at
least 72 hours. After heat treatment the materials were characterized with X-ray diffraction.
Laboratory button cells were fabricated in order to evaluate the electrochemical
properties of the lithium/manganese, bismuth mixed metal oxide electrochemical
system. The experimental cells were composed of a lithium anode separated from
a Teflon bonded cathode with a non-woven glass separator. The cathode was fabricated
by combining MnO
y (Bi
2O
3)
x, carbon
and Teflon in a 87:9:4 weight percent, respectively. The cathode mix was rolled
to 0.04 cm and dried in a vacuum oven. The cathode and 0.075 cm thick lithium foil
was cut using a 1.75 cm diameter (2.48 cm
2) hole punch. A 0.01 cm non-woven
glass was used for the separator and as a wick. The electrolyte used was 1 M LiPF
6
in proportional mixtures of dimethyl carbonate and ethylene carbonate.
The cells were cycled with an ARBIN Model BT-2043 Battery Test System. A two-step
charge profile was used. The charge profile consisted of a constant current charged
at 1.0, 2.0 and 4.0 mA to 4.2 volts followed by an applied constant voltage of
4.2 volts. The constant voltage was maintained for 5 hours or until the charge
current dropped to 0.1 mA. The cells were discharged at 1.0, 2.0 and 4 mA to 2.0
volts. A rest period of 15 minutes between charge and discharge cycles allowed
for the cells to equilibrate.
Prior to cycling cell impedance is recorded with a Solartron, SI1260 Frequency
Response Analyzer with a Solartron, SI1287 Electrochemical Interface using Scribner
Associates, Inc., ZPlot and ZView software. The data is used as a quality control
tool and for comparative use between variant chemistries.
The present invention encompasses a method of making a manganese mixed metal
oxide cathode for a lithium electrochemical system, comprising the steps of selecting
a bismuth compound from the group of bismuth compounds consisting of Bi
2O
3,
Bi(OH)
3 and Bi metal, mixing the bismuth compound with MnO
2,
heating the mixture in an annealing oven between 400° C. and 600° C.
for at least 72 hours, forming a positive, active manganese bismuth mixed metal
oxide compound having the general formula MnO
y (Bi
2O
3)
x,
where subscript x is greater than 0.05 and less than 0.25 and subscript y is about
2.0, drying the compound, forming a cathode by mixing the compound with a conductive
carbon and a binder, inserting the cathode into the lithium electrochemical system,
providing a reduced charge transfer impedance due to a catalytic reaction causing
the cathode to prevent an overcharge and a phase change and the compound remaining
reversible against a lithium compound in the lithium electrochemical system. Additionally,
the variations that apply to other embodiments of this invention also apply to
this method.
It is to be understood that although active starting material with a stoichiometry
of Bi
0.24MnO
2 was used to demonstrate the viability of this
material, other stoichiometries of MnO
y (Bi
2O
3)
x
could be used to optimize the cell performance. It should also be understood
that the sequence of heat treatments achieving the MnO
y (Bi
2O
3)
x
active material was used to demonstrate the viability of this material, other
sequences of MnO
y (Bi
2O
3)
x fabrication
could be used to optimize the cell performance. Additionally other metal oxides
used for lithium batteries could show improved performance by being reacted with bismuth.
It is to be further understood that other features and modifications to the foregoing
detailed description are within the contemplation of the present invention, which
is not limited by this detailed description. Those skilled in the art will readily
appreciate that any number of configurations of the present invention and numerous
modifications and combinations of materials, components, arrangements and dimensions
can achieve the results described herein, without departing from the spirit and
scope of this invention. Accordingly, the present invention should not be limited
by the foregoing description, but only by the appended claims.
*
