Lithium metal oxide electrodes for lithium cells and batteries

Details Lithium metal oxide electrodes for lithium cells and batteries Lithium metal oxide electrodes for lithium cells and batteries

2001-11-21

2004-01-20

Weiner, Laura (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Current producing cell, elements, subcombinations and...

Electrode

C429S231100, C429S231300, C429S223000, C429S231500, C429S231600, C423S599000

Reexamination Certificate

active

06680143

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to lithium metal oxide positive electrodes for non-aqueous lithium cells and batteries. More specifically, it relates to lithium-metal-oxide electrode compositions and structures, having in their initial state in an electrochemical cell, a general formula xLiMO
2
.(1−x)Li
2
M′O
3
alternatively Li
2−x
M
x
M′
1−x
O
3−x
in which 0<x<1 and where M is one or more ion with an average oxidation state of three and with at least one ion being Mn, and where M′ is one or more ions with an average oxidation state of four selected preferably from Mn, Ti and Zr; or, where M is one or more ion with an average oxidation state of three and with at least one ion being Ni, and where M′ is one or more ions with an average oxidation state of four with at least one ion being Mn. In one embodiment of the invention, the Mn content should be as high as possible, such that the LiMO
2
component is essentially LiMnO
2
modified in accordance with this invention. In a second embodiment of the invention, the Ni content should be as high as possible such that the LiMO
2
component is essentially LiNiO
2
modified in accordance with this invention. In a further embodiment of the invention, the transition metal ions and lithium ions may be partially replaced by minor concentrations of one or more mono- or multivalent cations such as H
+
derived from the electrolyte by ion-exchange with Li
+
ions, and/or Mg
2+
and Al
3+
to impart improved structural stability or electronic conductivity to the electrode during electrochemical cycling.
Prior application Ser. No. 09/887/842 filed Jun. 21, 2001 taught one or more cations M or M′ in a lithium metal oxide cathode, such as LiMO
2
or Li
2
M′O
3
where M has an oxidation state or valence of three and M′ has an oxidation state or valence of four. Although one of ordinary skill in the art would have clearly understood that the valences or oxidation states taught included ions which averaged oxidation state of three or average oxidation states of four, this continuation-in part application explictily states what was understood from the earlier filed '842 application and adds newly obtained data.
SUMMARY OF THE INVENTION
Lithium-metal oxide compounds of general formula LiMO
2
, where M is a trivalent transition metal cation such as Co, Ni, Mn, Ti, V, Fully executed, with a trivalent oxidation state and with electrochemically inactive substituents such as Al are very well known and are of interest as positive electrodes for rechargeable lithium batteries. The best-known electrode material is LiCoO
2
, which has a layered-type structure and is relatively expensive compared to the isostructural nickel and manganese-based compounds. Efforts are therefore being made to develop less costly electrodes, for example, by partially substituting the cobalt ions within LiCoO
2
by nickel, such as in LiNi
0.8
Co
0.2
O
2
or by exploiting the manganese-based system LiMnO
2
. Such layered compounds are sometimes stabilized by partially replacing the transition metal cations within the layers by other metal cations, either alone or in combination. For example, Li
+
and/or Mg
2+
ions may be introduced into the structure to improve the electronic conductivity of the electrode, or Al
3+
and/or Ti
4+
ions to improve the structural stability of the electrode at high levels of delithiation. Examples of such compounds are LiNi
0.8
Co
0.15
Al
0.05
O
2
and LiNi
0.75
CoO
0.15
Ti
0.05
Mg
0.05
O
2
.
A major problem of layered LiMO
2
compounds containing either Co or Ni (or both) is that the transition metal cations, M, with a trivalent oxidation state are oxidized during charge of the cells to a metastable tetravalent oxidation state. Such compounds are highly oxidizing materials and can react with the electrolyte or release oxygen. These electrode materials can, therefore, suffer from structural instability in charged cells when, for example, more than 50% of the lithium is extracted from their structures; they require stabilization to combat such chemical degradation.
Although the layered manganese compound LiMnO
2
has been successfully synthesized in the laboratory, it has been found that delithiation of the structure and subsequent cycling of the Li
x
MnO
2
electrode in electrochemical cells causes a transition from the layered MnO
2
configuration to the configuration of a spinel-type [Mn
2
]O
4
structure. This transformation changes the voltage profile of the Li/Li
x
MnO
2
cell such that it delivers capacity over both a 4V and a 3V plateau; cycling over the 3V plateau is not fully reversible which leads to capacity fade of the cell over long-term cycling. Other types of LiMnO
2
structures exist, such as the orthorhombic-form, designated O—LiMnO
2
in which sheets of MnO
6
octahedra are staggered in zig—zig fashion unlike their arrangement in layered LiMnO
2
. However, O—LiMnO
2
behaves in a similar way to layered LiMnO
2
in lithium cells; it also converts to a spinel-like structure on electrochemical cycling.
Therefore, further improvements must be made to LiMO
2
electrodes, particularly LiMnO
2
and LiNiO
2
, to impart greater structural stability to these electrode materials during electrochemical cycling in lithium cells and batteries. This invention addresses the stability of LiMO
2
electrode structures, particularly those in which M is Mn and Ni, and makes use of a Li
2
M′O
3
component in which M′ is one or more ions with an average oxidation state of four to improve their stability.


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