Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2000-04-21
2002-08-20
Dunn, Tom (Department: 1725)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S231950
Reexamination Certificate
active
06436574
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a nonaqueoue electrolyte secondary battery using a negative and a positive electrode, wherein: the negative electrode has its active material composed of metallic lithium, a lithium alloy, a carbonaceous material capable of doping and undoping a lithium ion, or like materials; and, the positive electrode has its active material composed of an oxide compound such as lithium manganese composite oxides or like materials. More particularly, the present invention relates to a nonaqueous electrolyte secondary battery, which is improved in: cycle life; charge and discharge properties at a high temperature; and, capacity retention properties thereof.
2. Description of the Related Art
A nonaqueous electrolyte secondary battery, for example such as a lithium ion secondary battery or a like, which is of an enclosed type, small in size and large in electric capacity, is used as a main power source for various electric and electronic appliances such as portable telephone sets, laptop computers, camcorders, or a like.
The nonaqueous electrolyte secondary battery is large in energy density (i.e., discharge capacity) per unit volume or weight, and capable of supplying a relatively high voltage, compared with a conventional aqueous electrolyte secondary. Consequently, the nonaqueous electrolyte secondary battery is expected to be widely used as a main power source not only for small-sized instruments, but also for large-scale plants.
In a so-called “lithium ion battery”: its negative electrode uses an active material such as a carbonaceous material or a like which is capable of doping and undoping a lithium ion; and, its positive electrode uses an active material, which is composed of a composite oxide of a transition metal combined with lithium. The negative and the positive electrode of the lithium ion battery are constructed of a negative and a positive current collecting strip element, respectively, wherein the strip elements are laminated through a separator interposed therebetween to form a current collector assembly which is coated with a suitable jacket material. It is also possible to form the current collector assembly by spirally winding the negative and positive collecting strip elements together with the separator interposed therebetween, wherein the current collector assembly thus formed is housed in a battery container, and thereby producing a battery product.
As a positive electrode active material of such a lithium ion secondary battery, there is a lithium manganese composite oxide, which is known in the art together with a lithium cobalt composite oxide. It is well known in the art that: when used at a temperature of from 40 to 60° C. and subjected to a repetition of charge and discharge operations, the lithium ion secondary battery employing the lithium manganese composite oxide has its charge and discharge cycle life considerably reduced in comparison with that employing the lithium cobalt composite oxide.
The problem to be solved by the present invention is as follows: namely, in order to solve the above problem of the battery which employs the lithium manganese composite oxide as its positive electrode active material, Japanese Laid-Open Patent Application No. Hei 7-153496 teaches to add, to the lithium manganese composite oxide, at least one compound selected from the group consisting of BaO, MgO, and CaO, and thereby preventing a manganese ion from dissolving into an electrolytic solution of the battery.
However, it is to be supposed that a reduction in the charge and discharge cycle life and deterioration in capacity retention properties of a lithium ion secondary battery (which employs the lithium manganese composite oxide, for example such as lithium manganate or like as its positive electrode active material) are caused by: deterioration in the positive electrode active material due to the dissoltion of the manganese ion from the lithium manganate; deposition of the thus dissolved manganese ion onto the surface of each of the negative electrode and the separator to plate the same surface; and, deterioration of the electrolytic solution of the battery. Consequently, it is difficult even for the above teaching of the Japanese Laid-Open Patent Application No. Hei 7-153496 to sufficiently solve the problem just mentioned above.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the present invention to provide a nonaqueous electrolyte secondary battery, which is excellent in its charge and discharge cycle characteristics, its capacity retention properties, and further in its safety in use.
According to a first aspect of the present invention, there is provided:
in a nonaqueous electrolyte secondary battery using a positive electrode active material, a negative electrode active material, and a nonaqueous electrolyte, wherein the positive electrode active material is a lithium manganese composite oxide, and the negative electrode active material is capable of doping and undoping a lithium ion, the improvement in its inside:
an oxide of at least one element selected from the group consisting of La, Sr, Nd, and Sm.
According to a second aspect of the present invention, there is provided:
in a nonaqueous electrolyte secondary battery using a positive electrode active material, a negative electrode active material, and a nonaqueous electrolyte, wherein the positive electrode active material is a lithium manganese composite oxide, and the negative electrode active material is capable of doping and undoping a lithium ion, the improvement comprising in its inside:
a carbonate of at least one element selected from the group consisting of La, Sr, Nd, and Sm.
According to a third aspect of the present invention, there is provided:
in a nonaqueous electrolyte secondary battery using a positive electrode active material, a negative electrode active material, and a nonaqueous electrolyte, wherein the positive electrode active material is a lithium manganese composite oxide, and the negative electrode active material is capable of doping and undoping a lithium ion, the improvement comprising in its inside:
a composite oxide of manganese combined with at least one element selected from the group consisting of La, Sr, Nd, and Sm.
In the foregoing, the preferable mode is one wherein the oxide, the carbonate or the composite oxide is contained in the positive electrode active material.
Also, the preferable mode is one wherein the nonaqueous electrolyte contains at least one compound selected from the group consisting of LiClO
4
, LiI, LiPF
6
, LiAlCl
4
, LiBF
4
, CF
3
SO
3
Li as its supporting salt.
Furthermore, the preferable mode is one wherein: the nonaqueous electrolyte is prepared by dissolving the supporting salt in a nonaqueous solvent, wherein concentration of the supporting salt in the nonaqueous solvent is within a range of from 0.8 to 1.5 mol/l.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The best modes for carrying out the present invention will be described in detail using embodiments of the present invention.
Present inventors have found that: in a nonaqueous electrolyte secondary battery (hereinafter may also be referred to as battery), it is possible to improve the battery in its charge and discharge cycle characteristics even when the battery is used at a high temperature, provided that the battery contains in its inside at least one of a predetermined oxide, a predetermined carbonate, and a lithium manganese composite oxide which is to be contained in its positive electrode active material, wherein the battery satisfies at least one of the following three conditions: that the predetermined oxide is an oxide of one element selected from the group consisting of La, Sr, Nd, and Sm; that the predetermined carbonate is a carbonate of one element selected from the group consisting of La, Sr, Nd, and Sm; and, that the lithium manganese composite oxide is a composite oxide of manganese combined with one element selected from the group consisting of La, Sr, Nd, and Sm. In t
Kambe Chika
Numata Tatsuji
Watanabe Mikio
Cooke Colleen P.
Dunn Tom
NEC Corporation
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