Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Utility Patent
1999-01-15
2001-01-02
Griffin, Steven P. (Department: 1754)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S223000, C429S231100, C429S231200, C429S231300, C429S220000, C429S231950, C428S701000, C428S702000
Utility Patent
active
06168887
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to layered lithium manganese oxide bronzes, to their production, and to electrodes comprising these bronzes, as well as use of those electrodes.
BACKGROUND OF THE INVENTION
Layered A
x
MnO
y
bronzes are classified into different categories, by Delmas et. al,
Revue de Chimie Minerale
19, 343 (1982); the categories are distinguished by the stacking of the oxygen: ABCABC . . . (03); II: ABBA . . . (P2); and III: ABBCCA . . . (P3). Those three different categories, O3, P2 and P3, are defined by a letter followed by a number: The letter may be O or P and refers to the oxygen environment of the alkali ion. The letter O refers to an octahedral environment of the alkali metal, while the letter P refers to a prismatic environment. The number indicates the number of MO
2
sheets within the unit cell; M in MO
2
refers to the 3d transition metal in the formula A
x
MO
y
; and M is Mn when the bronze is A
x
MnO
y
.
Layered bronzes and their structures are of interest as cathodes in rechargeable lithium batteries since layered structure types, more than any other, enable the reversible intercalation of lithium. The term “intercalation” herein means “the reversible insertion of guest atoms (Li, in this case) into host solids, such that the structure of the host is not significantly changed”. LiCoO
2
and LiNiO
2
are good examples of layered materials which are used in Li-ion batteries. The preparation of the corresponding LiMnO
2
is motivated by the fact that Mn is non-toxic and abundant. Unfortunately, solid-state reaction at high temperature to prepare layered LiMnO
2
has been unsuccessful since the non-layered structures LiMn
2
O
4
(spinel), LiMnO
2
(orthorhombic) or Li
2
MnO
3
(rocksalt) are more stable.
Layered LiMnO
2
of the O3 type has been prepared and reported by Armstrong and P. G. Bruce, Nature 381, 499 (1996). The layered LiMnO
2
samples were able to deintercalate large amounts of lithium, for example, Bruce and Armstrong reported 250 mAh/g, or about 90% of the Li atoms, on the first charge. Unfortunately the layered O3 phase converts to spinel during cycling, which leads to rapid capacity loss. Recently, the “direct” preparation of layered LiMnO
2
by a soft chemical route was reported by Tabuchi et al.
J. Electrochem. Soc.
145 L49-52 (1998), but their material also seems to convert to spinel upon cycling.
The layered O3 LiMnO
2
structure is very close to the structure (space group I4
1
/amd) of lithiated spinel Li
2
Mn
2
O
4
. The structures differ only by a minor cationic arrangement. Consequently, a conversion of layered LiMnO
2
of O3 structure to spinel during cycling can be expected. This is because the composition of Li
x
MnO
2
becomes equal to that of the thermodynamically stable phase, spinel LiMn
2
O
4
, at x=½.
Layered &agr;-NaMnO
2
exhibits an O3 structure. The O3 structure has octahedral sodium sites. Lithium prefers these octahedral sites. Therefore, the O3 structure can remain undisturbed during ion exchange. However, the P2 structure, with prismatic sodium sites, transforms to O2, and P3 transforms to O3, respectively. These transformations are possible since only a gliding of MnO
2
layers is required. Consequently, ion exchange of P3 manganese bronzes will finally lead to an O3 structure which is similar to the O3 structure obtained by ion exchanging an O3 sodium bronze. Layered lithium manganese oxides of the O3 type convert to spinel during cycling. Therefore, only ion exchange of manganese bronzes of different types than P3 or O3 is promising for Li-ion battery applications.
This work investigates lithium manganese oxides having the O2 structure obtained by ion exchange of P2-type sodium manganese bronzes. The O2 structure is very different from the spinel structure. The O3 structure has an oxygen stacking which differs fundamentally from P2. In O3 and spinel, all hexagonal close-packed O-M-O layers (M=cation) differ only by a translation, ABC→BCA; the O3 structure can transform gradually to spinel by minor changes in cation positions. In P2, every second layer is mirrored, ABC→CBA, and therefore different by symmetry. The same is true for O2. So the transformation of P2 or O2 to spinel can only occur by a rearrangement of the oxygen lattice which requires the breaking of all MnO bonds. This is highly unlikely at room temperature. Consequently it can be expected that lithium manganese oxide with the O2 structure will not be able to transform to spinel during battery operation. Its stacking will remain unchanged and it will cycle well.
Here the layered P2 structure is converted to O2 configuration. Moreover, it has been reported, by C. Delmas et al. in
Solid State Ionics
3/4, 165 (1981) and L. W. Schacklette et al.,
J. Electrochem. Soc.
145.2669 (1988), that P2 structures do not convert to O3 structures for sodium intercalation in Na
x
CoO
2
. Na
x
CoO
2
can be prepared in the three different crystal structures P2, O3 and P3. Starting the charge-discharge cycling of Na/Na
x
CoO
2
cells with either P3 or O3 Na
x
CoO
2
leads to the same voltage profile, proving that during cycling O3 and P3 transform to each other. The phase transformation is reversible and connected with a hysteresis between the charge and discharge voltage profiles. P2 structure Na
x
CoO
2
did not show a conversion to P3 or O3 based on the difference of its voltage profile.
SUMMARY OF THE INVENTION
For the first time a layered lithium manganese oxide was prepared which could be used as cathode material in lithium batteries without rapid transformation to spinel. These materials are based on the O2 structure which cannot transform to spinel without breaking all the Mn—O bonds in the sample. The O2 phases have a reversible capacity in the range of 150 mAh/g to 210 mAh/g if cycled between 2V and 4.8V vs. Li. These phases can be prepared by ion exchanging sodium manganese bronzes of the P2 type.
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C. Delmas et al., Revue de Chimie Minerale 19, 343 (1982).
C. Fouassier, et al., Materials Research Bulletin 10, 443 (1975).
A.R. Armstrong and P.G. Bruce, Nature 381, 499 (1996).
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Dahn Jeffrey R.
Paulsen Jens M.
Chemetals Technology Corporation
Griffin Steven P.
Strickland Jonas N.
Venable
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