Composite manganese oxide cathodes for rechargeable lithium...

Details Composite manganese oxide cathodes for rechargeable lithium... Composite manganese oxide cathodes for rechargeable lithium...

1999-03-31

2001-07-31

Weiner, Laura (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Current producing cell, elements, subcombinations and...

Electrode

C429S223000, C429S231950

Reexamination Certificate

active

06268085

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to compositions useful for energy conversion and storage. More particularly, it concerns a method of preparing a composite cathode suitable for use in lithium batteries. The composite cathode includes nanometer size particles of a lithium spinel oxide and a sodium manganese oxide.
2. Description of Related Art
Commercially available rechargeable lithium batteries often use lithium cobalt oxide as the cathode (Nagaura and Tozawa, 1990; Scrosati, 1992). But cobalt is expensive and relatively toxic. The high cost and toxicity of cobalt-based cathodes have created tremendous interest in the development of manganese-based cathodes, because manganese is much less expensive than cobalt and environmentally benign. In this regard, the spinel lithium manganese oxide LiMn
2
O
4
has been investigated extensively over the years (Thackeray et al., 1983; Tarascon et al., 1994).
LiMn
2
O
4
shows two plateaus in voltage versus capacity plots, one at around 4 V and the other at around 3 V. While the 4 V region generally shows good cyclability with a capacity of <120 mAh/g, the 3 V 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 3 V region of the stoichiometric LiMn
2
O
4
spinel (about 150 mAh/g, theoretically) cannot be utilized. More recently, attention has been focused on the synthesis of layered LiMnO
2
, but this material shows poor cyclability due to the transformation of the layer structure to the spinel structure upon prolonged cycling (Armstrong and Bruce, 1996; Vintins and West, 1997).
SUMMARY OF THE INVENTION
Described herein is a composite electrode and method of making same that addresses problems associated with LiMn
2
O
4
spinel cathodes. The composite in one embodiment comprises a mixture of nanometer size particles of a lithium spinel oxide, Li
1+x
Mn
2−x
O
4+&dgr;
, and a sodium manganese oxide, Na
y
MnO
2
, where, in one embodiment, 0≦x≦0.33, 0≦&dgr;≦0.5, and 0≦y≦1.0. Although the presence of excess oxygen (or cation vacancies), and possibly a substitution of some lithium for manganese in Li
1+x
Mn
2−x
O
4+&dgr;
, may reduce the capacity of the 4 V region, the capacity contribution from Na
y
MnO
2
leads to, in one embodiment, an overall reversible capacity of about 200 mAh/g in the range 4.3-2.3 V. Advantageously, this translates into an energy density that may exceed that of the currently utilized lithium cobalt oxide.
Advantageously, the presence of sodium manganese oxide Na
y
MnO
2
, on a nanometer scale, in a nanocomposite may help to overcome the difficulties posed by Jahn-Teller distortion and may lead to better cyclability in the 3 V region of the LiMn
2
O
4
spinel. A nanometer scale mixing of the component oxides in the composite is achieved, in one embodiment, by a solution-based chemical procedure. The procedure, in one embodiment, involves the reduction of sodium permanganate by lithium iodide at ambient temperatures in aqueous solutions followed by heating the product at around 500° C. in air. The relative amounts of Li
1+x
Mn
2−x
O
4+&dgr;
and Na
y
MnO
2
in the composite may be altered by changing the ratio of the reactants in the synthesis. Also, in one embodiment, sodium in Na
y
MnO
2
may be ion-exchanged with a lithium salt such as LiCF
3
SO
3
to give Na
y−&eegr;
Li
&eegr;
MnO
2+&dgr;
(0≦&eegr;≦y, where 0≦y≦1.0) or extracted with an oxidizing agent such as iodine to give Na
y−&eegr;
MnO
2+&dgr;
(0≦&eegr;≦y, where 0≦y≦1.0).
The electrochemical performance of the composite depends on the relative amounts of the two phases and the particle size, which in turn may be controlled by the firing temperature. It is contemplated that compositions manufactured according to the methods disclosed herein may exhibit excellent performance as cathodes in rechargeable lithium batteries. The composites may exhibit a capacity of about 200 mAh/g with excellent electrochemical cyclability in the range 4.3-2.3 V.
In one embodiment, reduction of sodium permanganate with sodium iodide instead of lithium iodide with appropriate modifications in quantity may be used to obtain Na
y
MnO
2+&dgr;
(0≦y≦1.0 and 0≦&dgr;≦0.5). Na
y
MnO
2+&dgr;
crystallizes in layer, tunnel or other structures depending on the value of x and &dgr; and the firing temperature, which in one embodiment may be about 200° C.≦T≦900° C. Ion exchange reactions of Na
y
MnO
2+&dgr;
with lithium salts such as LiCF
3
SO
3
or oxidative extraction of sodium with oxidizing agents such as iodine from Na
y
MnO
2+&dgr;
give Na
y−&eegr;
Li
&eegr;
MnO
2+&dgr;
and Na
y−&eegr;
MnO
2+&dgr;
, respectively. Na
0.44
MnO
2
cathodes with a tunnel structure are known to exhibit remarkable stability without transforming to spinel structure (Doeff et al., 1994; Doeff et al., 1996). Na
y
MnO
2+&dgr;
, Na
y−&eegr;
Li
&eegr;
MnO
2+&dgr;
and Na
y−&eegr;
MnO
2+&dgr;
(0≦y≦1, 0≦&eegr;≦1 and 0≦&dgr;≦0.5) cathodes obtained by procedures described herein exhibit high capacity with good electrochemical cyclability in lithium cells.
In one respect, the invention is a composite electrode material including a composite mixture of Li
1+x
Mn
2−x
O
4+&dgr;
and Na
y
MnO
2
, where 0≦x≦0.33, 0≦&dgr;≦0.5 and 0≦y≦1.
In other aspects, the Li
1+x
Mn
2−x
O
4+&dgr;
and the Na
y
MnO
2
may include nanometer size particles. As used herein, by “nanometer size particles”, or by “nanometer scale”, or by “nanocomposite” it is meant to refer to a range of sizes between about 5 nanometers and about 500 nanometers in diameter. The electrode material may include an oxidation state of manganese that lies in a range from about 3.0+ to about 4.0+.
In another respect, the invention is an electrode material including a two-phase composition of Li
1+x
Mn
2−x
O
4+&dgr;
and Na
y
MnO
2
, where 0≦x≦0.33, 0≦&dgr;≦0.5 and 0≦y≦1.0. The electrode material is prepared by a process including obtaining aqueous solutions of NaMnO
4
•H
2
O and LiI•3H
2
O at ambient temperatures; mixing the aqueous solutions together to obtain a precipitate; and heating the precipitate to from about 400° C. to about 800° C. for a period of time sufficient to form Li
1+x
Mn
2−x
O
4+&dgr;
and Na
y
MnO
2
in two phases.
In other aspects, the heating may include heating the precipitate to from about 500° C. to about 800° C. for a period of time sufficient to form Li
1+x
Mn
2−x
O
4+&dgr;
and Na
y
MnO
2
in two phases. The heating may include heating the precipitate to about 500° C. for a period of time sufficient to form Li
1+x
Mn
2−x
O
4+&dgr;
and Na
y
MnO
2
in two phases. The process may also include ion exchange of sodium in the Na
y
MnO
2
with a lithium salt. The lithium salt may include LiCF
3
SO
3
to produce Na
y−&eegr;
Li
&eegr;
MnO
2+&dgr;
, wherein 0≦&eegr;≦y. The process may also include extraction of sodium in the Na
y
MnO
2
with an oxidizing agent. The oxidizing agent may include iodine to produce Na
y−&eegr;
MnO
2+&dgr;
, wherein 0≦&eegr;≦y. The precipitate may be heated for about 24 hours in air. The precipitate may be heated for about 3 days in air. The molar ratio of NaMnO
4
•H
2
O:LiI•3H
2
O may be about 1:0.5. The molar ratio of NaMnO
4
•H
2
O:LiI•3H
2
O may be about 1:1. The molar ratio of NaMnO
4
•H
2
O:LiI•3H
2
O may be about 1:2. The molar ratio of NaMnO
4
•H
2
O:LiI•3H
2
O may be about 1:4. The molar ratio of NaMnO
4
•H
2
O:LiI•3H
2
O may be about 1:8.
In another respect, the invention is an electrode material including Na
y
MnO
2+&dgr;
, wherein 0≦y≦1.0 and 0≦&dgr;≦0.5. The electrod

Affiliated with

Also associated with

Rating

Composite manganese oxide cathodes for rechargeable lithium... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Composite manganese oxide cathodes for rechargeable lithium..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Composite manganese oxide cathodes for rechargeable lithium... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2560210