Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1998-01-07
2001-08-07
Weiner, Laura (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S224000, C429S223000, C429S221000, C429S231500, C429S231600, C429S218100, C429S304000
Reexamination Certificate
active
06270926
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to lithium secondary batteries employing spinel-structured lithium-manganese complex oxide as the cathode active material thereof.
2. Description of the Related Art
In the recent years, there has been accelerated development of down-sized and cordless design schemes in the field of electronics apparatus or equipment. In view of this trend, secondary batteries are of increasing interest since these have increased applicability as the power supply for such electronic equipment due to their capability of size reduction and high electrical energy density. The 4-V class lithium secondary batteries of the non-aqueous electrolytic solution type have been commercialized as secondary batteries satisfying the needs of the new equipment.
A lithium secondary battery generally includes (a) an cathode having a lithium-containing compound as the active material, (b) an anode having a material capable of absorbing and desorbing lithium, such as a carbon material, or lithium metal as the active material and (c) a separator containing a non-aqueous electrolytic solution or a solid electrolyte. The lithium-containing compound used as the active material of the cathode may include, for example, LiCoO
2
, LiNiO
2
and LiMn
2
O
4
. Recently, attention has been drawn to the spinel-structured lithium-manganese complex oxides, such as LiMn
2
O
4
, as the natural resource for the complex oxide because it is expected to exist in a large enough quantity to be inexpensive and provide a stable supply. Accordingly, various lithium secondary batteries comprising the complex oxide as an active material of the cathode has been proposed.
For example, Japanese Laid-Open Patent Application No. 6-333562 discloses a lithium secondary battery comprising an LiMn
2
O
4
type compound as the cathode active material, in which the compound is in the form of spherical particles having uniformly roughened surfaces and having a median diameter of from 0.5 to 0.6 &mgr;m while being distributed within a particle size range of 0.1 to 1.1 &mgr;m. Japanese Laid-Open Patent Application No. 8-69790 discloses a lithium secondary battery comprising a lithium-manganese complex oxide as the cathode active material, in which the complex oxide has specific surface area of from 0.05 to 5.0 m
2
/g.
However, the conventional lithium secondary batteries comprising such a spinel-structured lithium-manganese complex oxide as the active material are not still satisfactory with respect to the battery capacity and the charge-discharge cycle characteristics.
It is therefore an object of the present invention to provide a lithium secondary battery of large battery capacity with enhanced charge-discharge cycle characteristics.
SUMMARY OF THE INVENTION
A lithium secondary battery according to the preferred embodiments of the invention include an anode, a cathode and a separator containing non-aqueous electrolytic solution or a solid-state electrolyte interposed between the anode and the cathode. The anode comprises, as an active material, lithium metal, lithium alloy or a material capable of absorbing and desorbing lithium ions. The cathode comprises a spinel-structured lithium-manganese complex oxide as active material. The spinel-structured lithium-manganese complex oxide is in the form of hollow spherical secondary particles formed by sintering single crystal primary particles.
The primary particles preferably have an average diameter of from about 20 to 500 nm and the spinel-structured lithium-manganese complex oxide is preferably represented by a general formula: Li(Mn
2-x
Li
x
)O
4
(where 0≦x≦0.1).
According to present invention, the complex oxide used as the cathode active material of the lithium secondary battery has the shape of hollow spherical particles having many gaps which reach to the inside of the particles. Thus, the non-aqueous electrolytic solution can penetrate the inside of the particles, and the complex oxide has a large surface area. This makes it possible to improve the utilization efficiency of the cathode active material and increase battery capacity.
In addition, since the complex oxide is stable with respect to absorption and desorption of lithium due to the high crystallinity of the primary particles, the lithium secondary battery of the invention exhibits excellent charge-discharge cycle characteristics.
For the purpose of illustrating the invention, there is shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.
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“Preparation of Spherical LiCoO2Powders by the Ultrasonic Spray Decomposition and Its Application to Cathode Active Material in Lithium Secondary Battery”; Takashi Ogihara, et al.;Journal of the Ceramic Society of Japan; International Edition; 101 (1993) Oct.; No. 10; pp. 1128-1132.
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Hattori Koji
Yamashita Yasuhisa
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
Weiner Laura
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