Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1999-08-19
2004-03-16
Chaney, Carol (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C029S623100, C429S231100
Reexamination Certificate
active
06706443
ABSTRACT:
The present invention relates to a process for the preparation of a lithium manganese oxide by reacting at least one lithium compound and at least one manganese compound under hydrothermal conditions, that is to say from heated aqueous solutions under subatmospheric pressures, to a lithium manganese oxide of this type per se and to the use thereof as cathode material for electrochemical cells.
Processes for the preparation of lithium manganese oxides of the approximate composition LiMn
2
O
4
are known per se.
Thus, U.S. Pat. No. 4,980,251 describes a process for the preparation of a lithium manganese oxide of the formula Li
1−x
Mn
2
O
4
with 0≦x<1 by a solid phase reaction in which the corresponding lithium manganese oxide is obtained by mixing the corresponding oxides and/or carbonates together and heating the resulting mixtures in an oxidizing atmosphere to a temperature in the range from 200 to 600° C. This results, as stated in U.S. Pat. No. 4,980,251, in spinels with exceptionally high BET surface areas of, for example, more than 30 m
2
/g with, at the same time, poor crystallinity. Spinels of this type are said according to the publication to be particularly suitable for use in electrochemical cells.
DE-A-43 27 760 relates to a process for the preparation of a positive electrode for lithium secondary batteries whose active material consists of a lithium manganese oxide which has a spinel structure and which is obtained by mixing manganese dioxide with lithium formate and/or lithium acetate and subsequently heating the mixture at a temperature of from 550 to 800° C., followed by grinding.
Another process for the preparation of such oxides with a spinel structure is claimed in U.S. Pat. No. 5,135,732. In this case, firstly a gelatinous precipitate is formed by mixing stoichiometric amounts of an aqueous solution of lithium hydroxide and manganese acetate in the presence of a base at a pH of approximately 7. This precipitate is then dried at 60 to 150° C. to form a xerogel. Finally, the xerogel is heated to a temperature of from 200 to 600° C., resulting in a lithium manganese spinel.
DE-A 195 19 044 describes lithium- and manganese(III/IV)-containing spinels with a specific surface area of from 0.1 to 4 m
2
/g, and the use thereof as cathode material for electrochemical cells. The process indicated for the preparation of the spinels claimed therein is reaction of the starting compounds at elevated temperature.
However, the abovementioned processes have disadvantages with regard to the homogeneity of the resulting products. Furthermore, these processes often result in by-products which are unusable or usable only with difficulty, such as, for example, salts and off-gases.
Although the prior art publications discussed above also disclose the use of the oxides prepared therein as cathode material in electrochemical cells, the oxides with a spinet structure prepared by the prior art processes show a comparatively poor and often inadequate cycle stability on use as cathode material in electrochemical cells.
The use of LiCoO
2
and LiNiO
2
as cathode materials for electrochemical cells is the state of the art. Because of the relatively high material costs, the limited availability of cobalt, the environmental objections thereto and a potential danger associated with use of these compounds on overcharging, there is great interest in replacing the abovementioned compounds by, for example, lithium manganese oxides with a spinel structure, as also proposed in the prior art publications quoted above. Thus, for example, D. Fouchard et al. describe, in a scientific paper in “
The Electrochemical Society Proceedings”,
vol. 94-28, page 348, the use of lithium manganese oxides with a spinet structure in electrochemical cells.
In view of the above prior art, the object of the present invention is to provide a process which, on the one hand, makes it possible to prepare lithium manganese oxides, in particular inter alia pure-phase lithium manganese oxides with a spinet structure, and which furthermore can be carried out on the industrial scale without difficulty and with avoidance of by-products which cannot be utilized or are even hazardous, and results in lithium manganese oxides with very good electrochemical properties.
This object is achieved by a process for the preparation of a lithium manganese oxide of the formula Li
1.5−x
Mn
2
O
4
where the value of x satisfies the relation 0≦x<1.5, which comprises the following step: reaction of at least one lithium compound and at least one manganese compound, characterized in that the reaction is carried out in an aqueous medium at a temperature in the range from 80 to 500° C. under a pressure of from 1×10
5
Pa to 5×10
7
Pa.
As is evident from what has been said above, it is possible in the process according to the invention to obtain not only lithium manganese oxides with a spinel structure and the approximate composition LiMn
2
O
4
, but also oxides with a very small content of lithium, including &lgr;-MnO
2
. However, an oxide with a spinel structure is preferably obtained.
Although it is possible in principle to employ all lithium compounds in the process according to the invention, those preferably employed are Li
2
O, LiOH, LiCl, LiNO
3
, Li
2
CO
3
, Li carboxylates such as, for example, Li formates or Li acetate, or a mixture of two or more thereof.
There are also in principle no restrictions concerning the manganese compounds which can be employed in the process according to the invention. However, the manganese compound preferably employed is MnO
2
, MnO, MnOOH, Mn
2
O
3
, Mn
3
O
4
, MnCO
3
, Mn(NO
3
)
2
, Mn carboxylates such as, for example, Mn formate or Mn acetate or a mixture of two or more thereof, those employed being in particular oxidic manganese raw materials and manganese mixed oxides such as, for example, MnO, MnOOH, Mn
2
O
3
, Mn
3
O
4
and MnCO
3
, and mixtures of two or more thereof.
It is also possible furthermore for the lithium manganese oxides prepared according to the invention to contain in addition another metal M or a mixture of two or more other metals, preferably a metal of group IIa, IIIa, IVa, IIb, IIIb, IVb, VIb, VIIb or VIII of the Periodic Table, or a mixture of two or more thereof, and, in particular, iron, cobalt, nickel, titanium, boron, aluminium or a mixtureof two or more therof, resulting in oxides of the general formula
Li
1.5−x
M
z
Mn
2−z
O
4
,
where x is as defined above, and the value of z satisfies the relation 0.01≦z≦1.
Metal-doped Li—Mn-oxides of this type are prepared by employing in the reaction according to the invention a salt of a metal or a mixture of two or more thereof, as defined above, preferably an Fe, Co, Ni salt or a mixture of two or more thereof, in each case in the required amount.
Accordingly, the present invention also relates to a process for the preparation of a lithium manganese oxide of the formula Li
1.5−x
M
z
Mn
2−z
O
4
where the value of x satisfies the relation 0≦x≦1.5, M is a metal of group IIa, IIIa, IVa, IIb, IIIb, IVb, VIb, VIIb or VIII of the Periodic Table, or a mixture of two or more thereof, and the value of z satisfies the relation 0.01≦z≦1, preferably the relation 0.1≦z≦0.4, which comprises the following stage: reaction of at least one lithium compound, at least one manganese compound and at least one compound of a metal as defined above, characterized in that the reaction is carried out in an aqueous medium at a temperature in the range from 80 to 500° C. under a pressure of from 1×10
5
Pa to 5×10
7
Pa.
The lithium compound and manganese compound are preferably employed in an amount such that the manganese:lithium molar ratio is 2:approximately 1, although Mn:Li molar ratios of from 2:approximately 1.5 to approximately 2.5, preferably 2:approximately 1.3 to approximately 0.6, can also be chosen.
The special feature of the process according to the invention is to be regarded as being the reaction of the lithium compound and manganese compound unde
Krampitz Horst
Wohner Gerhard
Chaney Carol
Dove Tracy
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