Chemistry of inorganic compounds – Oxygen or compound thereof – Metal containing
Reexamination Certificate
1999-03-24
2002-03-26
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Oxygen or compound thereof
Metal containing
C423S594120, C423S595000, C423S596000, C429S223000, C429S224000
Reexamination Certificate
active
06361755
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to lithium batteries. More particularly, it concerns a method of preparing a spinel oxide suitable for use as a cathode in a lithium battery. The spinel oxide, Li
4
Mn
5
O
12
, is synthesized via a solution phase oxidation reaction followed by oven firing.
2. Description of Related Art
The high cost and high toxicity of cobalt has created enormous interest in development of less expensive, environmentally benign manganese-based cathodes as an alternative to cobalt-based cathodes for rechargeable lithium batteries. The spinel oxide LiMn
2
O
4
is being intensively pursued in this regard (Thackeray et al., 1983; Ohzuku et al., 1990; Thackeray et al., 1992; Tarascon et al., 1991; Gummow et al., 1994; Ferg et al., 1994; Yamada et al., 1995; Gao and Dahn, 1996a).
LiMn
2
O
4
shows two plateaus in voltage versus capacity plots, one around 4V and the other around 3V. While the 4V region generally shows good cyclability and ample capacity, the 3V region exhibits drastic capacity fading upon cycling due to the macroscopic volume change associated with a cooperative Jahn-Teller distortion. As a result, the capacity in the 3V region (about 150 mAh/g, theoretically) of the stoichiometric LiMn
2
O
4
spinel cannot be practically utilized.
It is known that the cyclability in the 3V region can be improved by increasing the average oxidation state of manganese through a substitution of lithium for manganese in Li
1+x
Mn
2
O
4
. Such substitutions may help to suppress Jahn-Teller distortions. For example, in the 3V region, the limiting case of x=0.33, corresponding to composition Li
4
Mn
5
O
12
is known to show better cyclability than the x=0 case corresponding to composition LiMn
2
O
4
. Although the increase in the oxidation state of manganese leads to a monotonic decrease in capacity in the 4 V region, it results in a better cyclability in the 3 V region, as cubic symmetry can be preserved to higher degrees of lithium insertion into the manganate lattice sites.
Li
4
Mn
5
O
12
may be unstable to heat treatment and may disproportionate to LiMn
2
O
4
and Li
2
MnO
3
at higher temperatures (Thackeray et al., 1992; Thackeray, Mansuetto, Dees and Vissers, 1996; Gao and Dahn, 1996b). This is significant in that Li
4
Mn
5
O
12
is generally synthesized by firing a mixture of manganese oxides or salts with lithium salts, and the diffusional limitations in such reactions necessitate higher firing temperatures (T>600° C.) in order for the reaction to go to completion.
Also, it is known that the oxidation state of manganese in the raw materials used to prepare spinel oxide materials is an important factor in determining the nature of the reaction product. For example, while raw materials with Mn
3+
tend to favor the formation of LiMn
2
O
4
, those with Mn
4+
help to stabilize Li
4
Mn
5
O
12
.
SUMMARY OF THE INVENTION
The present invention provides low temperature synthesis procedures for the preparation of Li
4
Mn
5
O
12
. The solution phase oxidation reaction disclosed herein employs lithium peroxide with lithium hydroxide and manganese acetate to obtain a precursor containing Mn
4+
. This precursor is preferably in the form of a precipitate. Advantageously, the use of a precursor containing Mn
4+
may favor the formation of Li
4
Mn
5
O
12
at low temperatures. In the method of the present invention, the precursor containing Mn
4+
may be fired at low to moderate temperatures (up to about 500° C.), causing it to lose water and yield Li
4
Mn
5
O
12
. Preferably the precursor is fired at temperatures of about 500° C. or less. Advantageously, the low firing temperatures of the present method may serve to preclude disproportionation of Li
4
Mn
5
O
12
to form LiMn
2
O
4
and Li
2
MnO
3
. As used herein, “low temperature” means a temperature of about 500° C. or less. As used herein, a precursor that is “fired” is heated. As used herein, a substance, such as a precursor, having a first temperature may be “heated” or may undergo “heating” by causing the temperature of the substance to rise relative to the first temperature.
Alternatively, hydrogen peroxide can be used instead of lithium peroxide and lithium carbonate can be used instead of lithium hydroxide with modifications in quantity that would be apparent to one of skill in the art. Advantageously, the general procedure described can be used with appropriate modifications, such as the use of manganese acetate with or without other metal acetates, that would be apparent to one of skill in the art to obtain other spinel cathodes such as Li
2
Mn
4
O
9−&dgr;
(0≦&dgr;≦1), Li
1+x
Mn
2−x
O
4+&dgr;
(0≦x≦0.33and 0≦&dgr;≦0.5)and Li
1+x
Mn
2-x-y
M
y
O
4+&dgr;
(0≦x≦0.33, 0≦y≦2.0, 0≦&dgr;≦0.5 and M=Cr, Fe, Co, Ni or Cu). The general procedure may also be used to produce other transition metal oxide cathodes such as LiCoO
2
, LiNiO
2
and LiNi
1−y
M
y
O
2
(M=Mn, Fe, Co or Cu). In this case, the procedure calls for the use of cobalt acetate or nickel acetate with or without other metal acetates, and a firing temperature of about 300° C. to about 900° C.
Surprisingly, the solution-based, low-temperature method described herein is able to access all Mn
4+
without oxygen vacancies in Li
4
Mn
5
O
12
. Samples synthesized according to the methods disclosed herein at T≦500° C. show excellent capacity retention in the 3V region with a maximum capacity of 160 mAh/g, which is close to the theoretical value.
It is contemplated that the materials prepared via the methods of the present invention may be useful as cathodes for rechargeable lithium batteries. It is further contemplated that the materials prepared via the methods of the present invention may be particularly well-suited for use in lithium polymer batteries. Advantageously, the Li
4
Mn
5
O
12
samples obtained by this low temperature approach exhibit a capacity close to the theoretical value, with excellent cyclability, making them well-suited for use as a cathode in a rechargeable lithium battery. The electrochemical characteristics of the samples also suggest possible use in electrochemical capacitor (supercapacitor) applications.
In a broad aspect, the invention is a process for forming a precipitate including admixing a first aqueous solution and a second aqueous solution with a third aqueous solution to produce the precipitate. As used herein, “admixing” means mixing or blending using any suitable means such as stirring, vibrating, shaking, agitating or the like. The first aqueous solution may include lithium peroxide or hydrogen peroxide. The second aqueous solution may include lithium hydroxide or lithium carbonate. The third aqueous solution may include manganese acetate.
In other aspects, the process may include filtering the precipitate and heating the precipitate to produce a spinel oxide. The spinel oxides disclosed herein are transition metal oxides. The process may also include grinding the spinel oxide to form a cathode. The admixing may include stirring. The precipitate may be heated to about 500° C. or less, and it may be heated at a rate of about 1° C./minute to about 10° C./minute. The precipitate may be heated to from about 300° C. to about 500° C., and it may be heated for about one to about five days. The precipitate may be allowed to dry in air at ambient temperature prior to being heated. The third aqueous solution may include manganese acetate without other metal acetates, and the spinel oxide may include Li
4
Mn
5
O
12
; Li
2
Mn
4
O
9−&dgr;
, where 0≦&dgr;≦1; or Li
1+x
Mn
2−x
O
4+&dgr;
, where 0≦x≦0.33 and 0≦&dgr;≦0.5. The third aqueous include manganese acetate with other metal acetates, such as chromium acetate, iron acetate, cobalt acetate, nickel acetate or copper acetate, for example, and the spinel oxide may include Li
1+x
Mn
2-x-y
M
y
O
4+&dgr;
, where 0≦x≦0.33, 0≦y≦2.0, 0≦&dgr;&lE
Kim Jaekook
Manthiram Arumugam
Board of Regents , The University of Texas System
Fulbright & Jaworski L.L.P.
Griffin Steven P.
Nguyen Cam N.
LandOfFree
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