Chemistry of inorganic compounds – Oxygen or compound thereof – Metal containing
Reexamination Certificate
1999-06-14
2001-08-28
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Oxygen or compound thereof
Metal containing
C423S605000, C429S224000
Reexamination Certificate
active
06280699
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to spinel Li
1+X
Mn
2−X
O
4+Y
intercalation compounds, and particularly to the use of spinel Li
1+X
Mn
2−X
O
4+Y
intercalation compounds in 4 V secondary lithium and lithium ion batteries.
BACKGROUND OF THE INVENTION
Heretofore, lithium intercalation compounds such as Li
1+X
Mn
2−X
O
4+Y
have been used in positive electrodes for 4 V secondary lithium and lithium ion batteries. The spinel LiMn
2
O
4
intercalation compound was first obtained by Wickham and Croft by heating lithium carbonate and manganese oxide in a 1:2 lithium to manganese molar ratio. D. G. Wickham and W. J. Croft,
Crystallographic and Magnetic Properties of Several Spinels Containing Trivalent
JA-1044
Manganese
; J. Phys. Chem. Solids 7, 351-360 (1958). As demonstrated in U.S. Pat. No. 4,426,253 to Hunter, the acid treatment of LiMn
2
O
4
forms a &lgr;-MnO
2
which can be used in a positive electrode for electrochemical power sources. It was later discovered that the spinel LiMn
2
O
4
could be used as the positive electrode for a secondary lithium cell. Thackery et al.,
Lithium Insertion Into Manganese Spinels
; Material Research Bulletin 18, 461-472 (1983).
The mean particle size and the particle size distribution are two of the basic properties characterizing the positive electrode intercalation materials for secondary lithium batteries. These properties are considered to be important because they directly influence the charge-discharge rate capability, the safety cell performance, the electrode formulation and the electrode coating process of positive electrodes containing these materials. In addition, a decrease in the mean particle size and distribution of the intercalation compounds typically results in an increase in the cycleability of these compounds. The reason for the increase in cycleability is that smaller particles are relatively more flexible than larger particles and therefore the changes in the crystal lattice parameters which occur during cycling do not damage the cycleability of the smaller particles to the degree that the larger particles are damaged.
Nevertheless, a decrease in the mean particle size results in a significant increase in the electronic resistivity of the spinel compounds. The electronic resistivity is controlled by the,contact resistivity between the particles which rises significantly due to an increase in the number of contact boundaries which the electrons have to overcome. The increase in electronic resistivity leads to an increase in the electrode polarization which decreases both the specific capacity and charge-discharge rate capability of the electrode. Furthermore, a decrease in the particle size is generally coupled with an unwanted decrease in the tapped or powder density. Because many batteries such as batteries for electronics have fixed volumes, it is preferred that the spinel material used in the positive electrode of these batteries has a high tapped density, so there is essentially more chargeable material in the positive electrode. A higher tapped density results in a positive electrode having a higher overall capacity. Therefore, depending on the nature of the intercalation compounds and the electrode formulation, the cycleability, specific capacity, tapped density and charge-discharge rate of the spinel material should be considered in determining a desirable particle distribution for the spinel material.
Accordingly, these factors have been considered in the preparation of LiCoO
2
intercalation compounds, where the desired particle size has been achieved by grinding the LiCoO
2
material. Nevertheless, grinding Li
1+X
Mn
2−X
O
4+Y
intercalation compounds results in a considerable reduction in specific capacity. V. Manev et al., Rechargeable Lithium Battery With Spinel-Related &lgr;-MnO
2
. Part III. Scaling-up Problems Associated With LiMn
2
O
4
Synthesis, J. Power Sources 54, 323-328 (1995). As described in this article, the reduction in specific capacity is due to changes in the Li
1+X
Mn
2−X
O
4+Y
structure which occur as a result of the stress of mechanical treatment, measured by the contraction of the crystal lattice parameter a. Therefore, grinding the Li
1+X
Mn
2−X
O
4+Y
material is not a desirable method of reducing the mean particle size and particle size distribution of spinel Li
1+X
Mn
2−X
O
4+Y
intercalation compounds.
SUMMARY OF THE INVENTION
The present invention provides a method of preparing a spinel Li
1+X
Mn
2−X
O
4+Y
intercalation compound having a predetermined mean particle size and particle distribution for 4 V secondary lithium and lithium ion cells having high cycleability, specific capacity, and charge-discharge rate capability.
The method of preparing the spinel Li
1+X
Mn
2−X
O
4+Y
intercalation compound comprises mixing at least one manganese compound with at least one lithium compound and firing the mixture in one or more steps within specific temperature ranges. The temperature ranges of the firing steps fall between about 450° C. and 900° C. with at least one firing step at a temperature of between about 700° C. and 900° C. to form the Li
1+X
Mn
2−X
O
4+Y
intercalation compound. Typically, the mean particle size of the lithium compound used to form the spinel is less than the mean particle size of the manganese compound thereby allowing the lithium particles to be uniformly dispersed with the manganese particles. Preferably, the manganese compound used to form the spinels has a predetermined mean particle diameter of between about 1 and 15 microns and a predetermined particle size distribution wherein at least about 99% of the particles have a diameter of less than about 40 microns. In addition, the manganese compounds preferably have a narrow particle size distribution wherein the maximum particle diameter is less than about 10 times the mean particle diameter and/or at least about 90% of the particles are distributed in a range not wider than about one order of magnitude.
The spinel Li
1+X
Mn
2−X
O
4+Y
intercalation compounds prepared according to the present invention have a predetermined mean particle size and particle size distribution generally corresponding to the size of the particles in the manganese compounds. Therefore, the predetermined mean particle size and particle size distribution is achieved without any additional mechanical treatment, e.g., grinding, of the spinel Li
1+X
Mn
2−X
O
4+Y
compounds. The Li
1+X
Mn
2−X
O
4+Y
intercalation compounds may be used in the positive electrodes of secondary lithium and lithium ion cells to provide cells having high cycleability, specific capacity and charge-discharge rate capability.
These and other features and advantages of the present invention will become more readily apparent to those skilled in the art upon consideration of the following detailed description and accompanying drawings which describe both the preferred and alternative embodiments of the present invention.
REFERENCES:
patent: 4246253 (1981-01-01), Hunter
patent: 4246324 (1981-01-01), de Nora et al.
patent: 4312930 (1982-01-01), Hunter
patent: 4366215 (1982-12-01), Coetzer et al.
patent: 4448856 (1984-05-01), Zuckerbrod et al.
patent: 4507371 (1985-03-01), Thackeray et al.
patent: 4546058 (1985-10-01), Charkey et al.
patent: 4599157 (1986-07-01), Suzuki et al.
patent: 4731309 (1988-03-01), Hoffman
patent: 4732741 (1988-03-01), Duncan et al.
patent: 4749634 (1988-06-01), Sammells
patent: 4828834 (1989-05-01), Nagaura et al.
patent: 4946664 (1990-08-01), Van Zyl et al.
patent: 4956247 (1990-09-01), Miyazaki et al.
patent: 4959282 (1990-09-01), Dahn et al.
patent: 4975346 (1990-12-01), Lecerf et al.
patent: 4980251 (1990-12-01), Thackeray et al.
patent: 5023155 (1991-06-01), Charkey et al.
patent: 5030523 (1991-07-01), Neat et al.
patent: 5110696 (1992-05-01), Shokoohi et al.
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patent: 51
Dow Stephen
Ebner Walter
Manev Vesselin
Thompson William
Alston & Bird LLP
FMC Corporation
Griffin Steven P.
Nguyen Cam N.
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