Manganese oxide based material for an electrochemical cell

Details Manganese oxide based material for an electrochemical cell Manganese oxide based material for an electrochemical cell

1999-08-09

2001-04-10

Nuzzolillo, Maria (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Current producing cell, elements, subcombinations and...

Electrode

C429S231900, C429S218100, C423S599000, C423S179500

Reexamination Certificate

active

06214493

ABSTRACT:

FIELD OF THE INVENTION
This invention concerns electrochemical cells and relates to a novel layered material for use in such cells, a method for producing the layered material, and a cell having the layered material as the positive electrode.
BACKGROUND OF THE INVENTION
Electrochemical cells generally have a negative electrode, a positive electrode, and an electrolyte placed between the electrodes. The electrolyte is chosen so that transfer of ions between the two electrodes occurs, thus producing an electrical current. One example of an electrochemical cell is a rechargeable battery. The use of non-layered LiMnO
2
in secondary batteries is proposed in JP 6036799. The use of layered materials such as lithium cobalt oxide, LiCoO
2
, as the positive electrode in such a rechargeable battery is well established. The layered material LiCoO
2
consists of sheets of oxygen ions stacked one on top of the other. Between the first and second layers of oxygen are located the cobalt ions, with the lithium ions being located between the second and third oxygen layers. Use of LiCoO
2
in rechargeable batteries allows greater energy storage per unit weight and volume than is possible in conventional rechargeable batteries such as nickel-cadmium. However LiCoO
2
has disadvantages in that it is somewhat toxic, has limited energy storage capacity, and the cobalt containing materials from which it is produced are expensive and scarce.
Attempts have been made to use other compounds with a similar layered structure to that of LiCoO
2
, such as LiNiO
2
, and LiFeO
2
. EP 0 017 400 discloses a range of compounds having layers of the &agr;-NaCrO
2
structure and GB 2242898 discloses a range of compounds with a layering intermediate that of a ABO
2
structure and a spinel-type structure A(B
2
)O
4
. However, preparation of the materials according to the present invention is not taught and could not be achieved; see for example E. Rossen, C. D. W. Jones, and J. R. Dahn, “Structure and electrochemistry of Li
x
Mn
y
Ni
1-y
O
2
”, Solid State Ionics, 57 (1992), 311-318.
It is one aim of the present invention to provide a novel layered manganese oxide material which can be used in electrochemical cells.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, there is provided a manganese oxide material, wherein the material is of the form Q
q
Mn
y
M
z
O
2
, where Q is any Group I element, i.e. K, Li, Rb, M is any element, y is any number greater than zero, q and z are each any number greater than or equal to zero, and the material has a layered structure.
A layered structure is one in which the ions are arranged in a series of generally planar layers, or sheets, stacked one on top of another. In general, each layer contains ions of one particular element, although the layer of Mn ions may contain M ions if present. Thus, when z is equal to zero and q is greater Man zero, the layering will consist of sheets of oxide ions which are separated by alternating layers of Q ions and Mn ions, i.e. the layers order as a layer of oxide ions, a layer of Mn ions, a layer of oxide ions, a layer of Q ions and a layer of oxide ions; this is repeated throughout the structure.
Where z is not equal to zero, y+z is preferably chosen to equal one. In such a material, the M ions will occupy sites in the Mn layers.
Where z is not equal to zero, the element M is typically chosen from Group II elements, the transition elements or from Group III elements. Suitable elements include Be, Mg, Ca, Sc, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Al, Ga, P.
Accordingly in a particularly preferred material according to the invention, Q is an alkali metal ion, such as Rb, K or Li, and M is a transition metal ion.
Preferably Q is chosen to be Li, so that the material is of the form Li
w
Mn
y
M
z
O
2
, where w is any number greater than zero.
The layered structure preferably possesses a crystal symmetry lower than rhombohedral. A preferred symmetry for the layered structure is monoclinic. The monoclinic structure possesses one 2-fold axis and/or one plane of symmetry, its unit cell possessing three unequal axes, one axis being perpendicular to the other two axes which are inclined at an oblique angle, &bgr;. In such a structure the Mn ions are not equally spaced from all nearest neighbour oxide ions, i.e. the three oxide ions in the adjacent upper layer and the three oxide ions in the adjacent lower layer, but rather are distorted from equal spacing so that the Mn—O bond distance varies. An equivalent view of this is that the layered structure comprises layers of MnO
6
polyhedra separated by layers of other ions, for example lithium ions.
Preferably the material is LiMnO
2
, having a layered monoclinic structure.
In a simple alternative the material may be of the form Mn
y
O
2
, where the layers order as a layer of oxide ions, a layer of Mn ions; this being repeated throughout the structure. The layered structure of this material is rhombohedral, with the Mn ions being equally spaced from all nearest neighbour oxide ions, i.e. the three oxide ions in the adjacent upper layer and the three oxide ions in the adjacent lower layer, so that the Mn—O bond distance is constant. An equivalent view of this is that the layered structure comprises successive layers of MnO
6
octahedra.
According to a further aspect of the invention, there is provided a method of preparing a manganese oxide material of the invention, comprising processing an intermediate material X
x
Mn
y
M
z
O
2
, where X is a Group I element not being lithium, M is any element, x and y are each any number greater than zero, and z is any number greater than or equal to zero, by an ion exchange reaction with a reactant containing lithium ions, so as to replace X with lithium and produce a material of the form Li
w
Mn
y
M
z
O
2
, where w is any number greater than zero, and the material has a layered structure.
Preferably X is chosen to be Na, so that the intermediate material is of the form Na
x
Mn
y
M
z
O
2
.
More preferably y is equal to one and z is equal to zero, so that the intermediate material is of the form NaMnO
2
. The use of such an intermediate material results in production of a layered material of the form LiMnO
2
, having a layered monoclinic structure as described above.
The reactant may be any suitable lithium salt, such as LiBr or LiCl. Preferably the ion exchange reaction is achieved by heating the reactant and intermediate material under reflux. Typically n-pentanol, n-hexanol or n-octanol are used as the reflux agent, with the reflux period being 6-8 hours.
According to a further aspect of the invention, there is provided a method of preparing a manganese oxide material of the invention, comprising processing a precursor material Q
q
Mn
y
M
z
O
2
, where Q and M are each any element, q and y are each any number greater than zero, and z is any number greater than or equal to zero, by carrying out an ion If removal reaction, so as to remove Q and produce a material of the form MN
y
M
z
O
2
, with a layered structure.
Ion removal is conveniently achieved by electrochemical extraction, using the precursor material as the working electrode in an electrochemical cell. This is of particular advantage in preparation of materials of the form Mn
y
O
2
. For preparation of these materials, Q is preferably chosen from the Group I elements, such as Na, K, Rb. The Mn
y
O
2
may be subsequently processed to insert lithium so as to produce Li
w
Mn
y
O
2
.
According to another aspect of the invention, there is provided an electrochemical cell, wherein the positive electrode is of the form Li
q
Mn
y
M
z
O
2
, where M is any element, y is any number greater than zero, and q and z are each any number greater than or equal to zero. The use of the manganese in the electrode avoids the need for use of cobalt or nickel which is of advantage as manganese is less toxic, more abundant and cheaper than cobalt and nickel.
Preferably y and q are equal to one, and z is equal to zero, with the preferred electrode material being LiMnO
2
.
A rechargeable battery is an example of an ele

Affiliated with

Also associated with

Rating

Manganese oxide based material for an electrochemical cell does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Manganese oxide based material for an electrochemical cell, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Manganese oxide based material for an electrochemical cell will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2442075