Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2000-06-05
2003-09-30
Weiner, Laura (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S231100, C429S231950, C429S322000, C429S323000, C429S330000, C429S338000, C429S337000, C429S339000, C429S340000, C429S342000
Reexamination Certificate
active
06627351
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a non-aqueous electrolyte battery incorporating a positive-electrode active material constituted by a composite lithium oxide.
2. Description of the Related Art
In recent years, considerable progress of a variety of electronic apparatuses has been made. Therefore, rechargeable secondary batteries have been studied which can conveniently be used for a long time with low cost. Representative secondary batteries are exemplified by a lead battery, an alkali battery and a lithium secondary battery. In particular, the lithium secondary battery has advantages of high output and a high energy density. The lithium secondary battery incorporates positive and negative electrodes, to which lithium ions can reversibly be doped/dedoped, and non-aqueous electrolytic solution.
The capacities of the lithium secondary batteries have been enlarged recently. On the other hand, reduction in the cost has been attempted by selecting materials. In particular, a cobalt oxide which has been employed to constitute the positive electrode is a costly material as compared with other oxides of nickel, manganese and iron. Therefore, alternative employment of a relatively low-cost metal oxide has been required. In particular, employment of a manganese oxide which is one of transition metal materials exhibiting lowest cost to constitute the positive electrode has been required. As a representative manganese oxide, a spine compound LiMn
2
O
4
is known. The theoretical capacity of the foregoing compound is smaller than 150 mAh/g which is smaller than 274 mAh/g of LiCoO
2
. The reason for this lies in that LiMn
2
O
4
contains Li atoms, the number of which is half of Li atoms in LiCoO
2
which include Li atoms by the same number as those in transition metal.
Therefore, LiMnO
2
having a theoretical capacity equivalent to that of LiCoO
2
has energetically been studied as a candidate of the positive-electrode active material containing manganese. According to reports of studies in the early stage, high-temperature LiMnO
2
and low-temperature LiMnO
2
have been reported.
High-temperature LiMnO
2
has first been reported by W. D. Johnston et al. (J. Am. Chem. Soc., 78, 325 (1956)). Then, R. Hoppe, G. Brachtel and M. Jansen (Z. Anorg. Allg. Chmie, 417, 1 (1975) have determined the structure. Low-temperature LiMnO
2
has first been reported by T. Ozuka, A. Ueda and T. Hirai (Chem. Express, Vol. 7, No. 3, 193 (1992)).
Each of high-temperature LiMnO
2
and low-temperature LiMnO
2
has a structure incorporating orthorombic lattices and defined by space group Pmnm. The theoretical capacity of each of the high-temperature LiMnO, and low-temperature LiMnO
2
is about 300 mAh/g. The theoretical capacity cannot be realized when the charge/discharge conditions which are adapted to the present non-aqueous electrolyte batteries are employed.
According to the foregoing documents, the charge capacity of high-temperature LiMnO
2
is 150 mAh/g and that of the low-temperature LiMnO
2
is 200 mAh/g. The initial discharge capacity of high-temperature LiMnO
2
is not higher than 50 mAh/g (2.0 V≧V (Li/Li
+
), while that of low-temperature LiMnO, is 190 mAh/g (2.0 V≧V (Li/Li
+
)).
The foregoing values are those measured when the current density is 100 &mgr;A/cm
2
or lower. To practically employ the foregoing manganese oxides, the foregoing values must be realized when the current density is 500 &mgr;A/cm
2
or higher. When the foregoing manganese oxide is used at the high-load current density, the discharge capacities of the high-temperature LiMnO
2
and the low-temperature LiMnO
2
are reduced to about 40 mAh/g and about 120 mAh/g, respectively.
The foregoing phenomenon are caused from the following two factors. That is, each material has a crystralline structure as shown in
FIG. 1
that sheets each of which is constituted by Mn—O are laminated such that Li is introduced between the Mn—O sheets. The foregoing crystalline structure, however, has the diffusion paths for Li formed into a zigzag shape. Thus, quick diffusion of Li cannot be observed. Another reason lies in that the high-temperature LiMnO
2
has high crsytallinity. Therefore, the electron resistance caused from impurity failure is low. On the other hand, low-temperature LiMnO
2
having low crystallinity encounters high resistance caused from impurity. Therefore, low-temperature LiMnO
2
encounters considerable IR drop owing to a high load, that is, a high current density. Therefore, great energy loss occurs. Under the foregoing circumstances, LiMnO
2
having a flat layer structure permitting quick diffusion of Li and exhibiting high crystallinity has been required.
In 1996, Armstrong et al. has prepared LiMnO
2
, having space symmetry of C2/m by ion-substituting Na of NaMnO
2
(A. R. Armstrong et aluminum., Nature, 381,499 (1996)). Thus, a first report about LiMnO
2
having the flat structure has been made. Then, in 1998, a report has been made that the same structure as that of LiMnO
2
reported by Armstrong et al. can be obtained by performing preparation of LiMn
0.75
.,Al
0.25
O
2
such that partial pressure of oxygen is controlled (Y. Jang et aluminum., Electrochemical and Solid-State Letters, 1, (1) 13 (1998)). The reported compound, which has been prepared at high temperatures, has high crystallinity. Moreover, enlargement of the capacity under a high load has been expected owing to the flat diffusion paths for Li.
Each LiMnO
2
encounters change in the structure (formed into a spinel structure) during the charging process, causing the discharge capacity to be reduced. In particular, LiMnO
2
of the type reported by Armstrong et al. encounters considerable change in the structure during the charging process. Thus, a satisfactorily large discharge capacity cannot be obtained.
On the other hand, a consideration is made that LiMn
0.75
Al
0.25
O
2
is not thermodynamically unstable as compared with LiMnO
2
. As compared with LiMnO
2
, change in the structure does not considerably occur. However, formation of a solid solution of Al which is electrochemically inactive results in reduction in the capacity.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the present invention to provide a non-aqueous electrolyte battery free from considerable change in the structure of a positive-electrode active material thereof and capable of enlarging the capacity thereof.
To achieve the object, according to one aspect of the present invention, there is provided a non-aqueous electrolyte battery comprising: a positive electrode containing a positive-electrode active material; a negative electrode containing a negative-electrode active material to which Li can be doped/dedoped; and a non-aqueous electrolyte disposed between the positive electrode and the negative electrode and containing non-aqueous solvent and an electrolyte, wherein a material expressed by general formula LiMn
1−y
Al
y
O
2
, (0.06≦y<0.25) is contained as the positive-electrode active material and LiMn
1−y
A
1−y
O
2
has a crystalline structure expressed by space group C2/m.
The non-aqueous electrolyte battery according to the present invention and incorporating a layered compound expressed by LiMn
1−y
Al
y
O
2
is able to enhance diffusion of lithium ions. Since the non-aqueous electrolyte battery according to the present invention is structured such that the value of y of LiMn
1−y
Al
y
O
2
is specified, deterioration in the electric conductivity can be prevented. Moreover, thermal stability of the crystalline structure can be improved.
REFERENCES:
patent: 6030726 (2000-02-01), Takeuchi et al.
Sonnenschein Nath & Rosenthal LLP
Sony Corporation
Weiner Laura
LandOfFree
Non-aqueous electrolyte battery does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Non-aqueous electrolyte battery, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Non-aqueous electrolyte battery will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3012647