Lithium cobalt oxides and methods of making same

Details Lithium cobalt oxides and methods of making same Lithium cobalt oxides and methods of making same

2000-12-07

2003-06-17

Kopec, Mark (Department: 1751)

Compositions

Electrically conductive or emissive compositions

Metal compound containing

C252S518100, C429S218100, C429S231300, C429S231950, C429S223000, C429S224000, C429S322000, C429S209000, C423S594120, C423S599000, C423S617000, C423S624000, C423S635000, C423S641000

Reexamination Certificate

active

06579475

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to lithium cobalt oxides for use as positive electrode materials for rechargeable lithium and lithium-ion secondary batteries, and to methods of making lithium cobalt oxides.
BACKGROUND OF THE INVENTION
LiCoO
2
is currently being used in over 95% of commercial lithium and lithium-ion secondary batteries as the active positive electrode material. The current production rate of lithium and lithium-ion batteries is about 30 million units per month with each unit containing about 10-15 g of LiCoO
2
(i.e., 300-450 metric tons/month).
LiCoO
2
can be made by a number of different methods by reacting a lithium salt and a cobalt salt. However, these methods often involve lengthy reaction times thereby reducing the rate of LiCoO
2
production.
Therefore, there is a need in the art to provide a method of preparing LiCoO
2
that demonstrates good performance in rechargeable lithium and lithium-ion secondary batteries and that can be produced with a relatively short reaction time.
SUMMARY OF THE INVENTION
The present invention includes lithium cobalt oxides having hexagonal layered crystal structures and methods of making same. The lithium cobalt oxides of the invention have the formula Li
w
Co
1−x
A
x
O
2+y
wherein 0.96≦w≦1.05, 0≦x≦0.05, −0.02≦y≦0.02 and A is one or more dopants. Preferably, 0.98≦w≦1.02 and 0≦x≦0.02.
The lithium cobalt oxides of the invention preferably have a position within the principal component space defined by the following relationship:
ax
i
+by
i
≦c
wherein x
i
={right arrow over (S)}
i
&Circlesolid;{right arrow over (P)}
c1
; y
i
={right arrow over (S)}
i
&Circlesolid;{right arrow over (P)}
c2
; the vector {right arrow over (S)}
i
is the x-ray spectrum for the Li
w
Co
1−x
A
x
O
2+y
compound; the vectors {right arrow over (P)}
c1
and {right arrow over (P)}
c2
are determined by measuring the x-ray powder diffraction values {right arrow over (S)}
i
between 15° and 120° using a 0.020 step size and CuK&agr; rays for a large sample set of lithium cobalt oxides and using the regression of {right arrow over (S)}
i
of the sample set against the capacity fade after 50 cycles of a lithium coin cell that includes a lithium negative electrode and the lithium cobalt oxide as the positive electrode material and that is cycled between 3.0 and 4.3V at a constant current of C/3 during both charge and discharge cycles; and the values a, b and c are determined by using only the x
i
and y
i
values for Li
w
Co
1−x
A
x
O
2+y
compounds in the sample set that have a capacity fade after 50 cycles of less than or equal to 15%.
More preferably, the lithium cobalt oxides of the invention have a position within the principal component space defined by the following relationship:
x
i
+0.77
y
i
≦−6
wherein x
i
={right arrow over (S)}
i
&Circlesolid;{right arrow over (P)}
c1
; y
i
={right arrow over (S)}
i
&Circlesolid;{right arrow over (P)}
c2
; {right arrow over (S)}
i
is the x-ray spectrum for the Li
w
Co
1−x
A
x
O
2+y
compound; and {right arrow over (P)}
c1
and {right arrow over (P)}
c2
are determined by measuring the x-ray powder diffraction values sh between 15° and 120° using a 0.020 step size and CuK&agr; rays for a large sample set of lithium cobalt oxides and using the partial least squares regression (PLSR) of {right arrow over (S)}
i
of the sample set against the capacity fade after 50 cycles of a lithium coin cell that includes a lithium negative electrode and the lithium cobalt oxide as the positive electrode material and that is cycled between 3.0 and 4.3V at a constant current of C/3 during both charge and discharge cycles. For example, {right arrow over (P)}
c1
and {right arrow over (P)}
c2
can be defined by the coefficients provided in Table 1 (wherein 2&thgr; is the scattering angle of x-ray powder diffraction measurements using CuK&agr; rays).
The lithium cobalt oxides of the invention can be used in the positive electrode of a rechargeable lithium or lithium-ion secondary battery in accordance with the invention. For the lithium cobalt oxides of the invention, the capacity fade of a lithium coin cell having a lithium negative electrode and using the lithium cobalt oxide as the positive electrode material when cycled between 3.0 and 4.3V at a constant current of C/3 during both charge and discharge cycles after 50 charge/discharge cycles is preferably less than or equal to 15%, more preferably less than or equal to 10%. Moreover, the initial specific discharge capacity is preferably greater than or equal to 154 mAh/g.
The lithium cobalt oxides of the invention are prepared by heating a lithium source compound, a cobalt source compound and optionally one or more source compounds that include dopants A at a temperature below about 850° C. to produce Li
w
Co
1−x
A
x
O
2+y
and heating the Li
w
Co
1−x
A
x
O
2+y
compound at a temperature from about 900° C. and 1000° C. to form and enhance the hexagonal layered crystal structure of the Li
w
Co
1−x
A
x
O
2+y
compound. The temperature in the first heating step is preferably from about 500° C. to about 850° C. and the temperature in the second heating step is preferably from about 950° C. to about 980° C. The source compounds in the first heating step can be heated at more than one temperature below about 850° C. In addition, the Li
w
Co
1−x
A
x
O
2+y
compound in the second heating step can be heated at more than one temperature from about 900° C. to about 1000° C. Preferably, the first heating step comprises heating the source compounds for a period of time of from about 30 minutes to about 3 hours and the second heating step comprises heating the source compounds for a period of time of from about 30 minutes to about 7 hours. The lithium source compound preferably used with the invention is selected from the group consisting of Li
2
CO
3
and LiOH and the cobalt source compound is preferably selected from the group consisting of Co
3
O
4
and Co(OH)
2
. The lithium cobalt oxide is preferably cooled after the heating steps at a rate of from 8° C./min to 140° C./min, more preferably from 10° C./min to 100° C./min.
The present invention further includes a method of analyzing a compound to determine if the compound is suitable for use as the active positive electrode material in a lithium or lithium-ion secondary battery. The method of the invention comprises determining a principal component space defined by the relationship ax
i
+by
i
≦c, wherein x
i
={right arrow over (S)}
i
&Circlesolid;{right arrow over (P)}
c1
; y
i
={right arrow over (S)}
i
&Circlesolid;{right arrow over (P)}
c2
; the vector {right arrow over (S)}
i
is the x-ray spectrum for the compound; the vectors {right arrow over (P)}
c1
and {right arrow over (P)}
c2
are determined by measuring the x-ray powder diffraction values {right arrow over (S)}
i
for a predetermined range of 2&thgr; values using a predetermined step size by sampling a plurality of samples of compounds having the same general formula as the compound and using the regression of {right arrow over (S)}
i
of the sample set against predetermined battery performance data for the samples by incorporating the samples as the positive electrode active material in a lithium or lithium-ion secondary battery. The x
i
and y
i
values for the compounds in the sample set that have the predetermined battery performance data are then used to determine a, b and c. The compound is analyzed by measuring the x-ray diffraction spectra for the compound to obtain x and y values and determining whether the x and y values meet the relationship ax
i
+by
i
≦c and thus whether the compound possesses the battery performance and x-ray diffraction spectra suitable for use as the active positive electrode material.
The lithium cobalt oxides of the invention have good cycleability properties including good initial specific capacities and capacity fades

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